Chapter 1 The History and Scope of Epidemiology.

Chapter 1 The History and Scope of Epidemiology

Tap Water Increases Miscarriages
Swan et al. (1998) released results on total trihalomethanes (TTHMs) in drinking water. Human exposure to TTHMs may be related to adverse pregnancy outcomes.

Bioterrorism-Associated Anthrax Cases
Index case reported in Florida. Additional cases, including fatal cases, reported in New York, New Jersey, Connecticut. Contaminated mail linked to some of the cases.

Epidemiology Defined Epidemiology derives from "epidemic," a term which provides an immediate clue to its subject matter. Epidemiology originates from the Greek words, epi (upon) + demos (people) + logy (study of). 3

Definition of Epidemiology
Epidemiology is concerned with the distribution and determinants of health and diseases, morbidity, injuries, disability, and mortality in populations. 4

Key Aspects of This Definition
Determinants Distribution Population Health phenomena Morbidity and mortality 5

Determinants Factors or events that are capable of bringing about a change in health. 6

Examples of Determinants
Biologic agents--bacteria Chemical agents--carcinogens Less specific factors--stress, drinking, sedentary lifestyle, or high-fat diet

The Search for Determinants
Outbreak of Fear--Ebola virus in Kikwit, Zaire Fear on Seventh Ave.--Legionnaires’ disease in New York City Red Spots on Airline Flight Attendants--dye from life vests 7

Distribution Frequency of disease occurrence may vary from one population group to another. 8

Disease Distribution Examples
Hypertension more common among young black men than among young white men. Coronary heart disease occurrence differs between Hispanics and non-Hispanics.

Population Epidemiology examines disease occurrence among population groups, not individuals. Epidemiology is often referred to as population medicine. The epidemiologic description indicates variation by age groups, time, geographic location, and other variables. 9

Health Phenomena Epidemiology investigates many different kinds of health outcomes: Infectious diseases Chronic diseases Disability, injury, limitation of activity Mortality Active life expectancy Mental illness, suicide, drug addiction 10

Morbidity and Mortality
Morbidity--designates illness. Mortality--refers to deaths that occur in a population or other group. Note that most measures of morbidity and mortality are defined for specific types of morbidity or causes of death. 11

Aims and Levels To describe the health status of populations.
To explain the etiology of disease. To predict the occurrence of disease. To control the occurrence of disease. 12

Foundations of Epidemiology
Interdisciplinary Methods and procedures--quantification Use of special vocabulary Epidemic frequency of disease 13

Epidemiology Is Interdisciplinary
Epidemiology is an interdisciplinary field that draws from biostatistics and the social and behavioral sciences, as well as from the medically related fields of toxicology, pathology, virology, genetics, microbiology, and clinical medicine. 14

Quantification Quantification is a central activity of epidemiology.
Epidemiologic measures often require counting the number of cases of disease. Disease distributions are examined according to demographic variables such as age, sex, and race. 15

Epidemic “The occurrence in a community or region of cases of an illness (or an outbreak) clearly in excess of expectancy…” Relative to usual frequency of the disease. 17

Infectious Disease Epidemics
A single case of a long absent communicable disease. First invasion of a communicable disease. Two cases of such a disease associated in time and place are sufficient evidence of transmission to be considered an epidemic. 18

Concept of Epidemic and Non-infectious Diseases
Some examples that use the concept of an epidemic are: Love Canal Brown lung disease Asbestosis among shipyard workers Diseases associated with lifestyle

Pandemic “ an epidemic on a worldwide scale; during a pandemic, large numbers of persons may be affected and a disease may cross international borders.” An example is a flu pandemic.

Ascertainment of Epidemics
Surveillance Epidemic threshold 19

Surveillance The systematic collection of data pertaining to the occurrence of specific diseases. Analysis and interpretation of these data. Dissemination of disease-related information.

Epidemic Threshold The minimum number of cases (or deaths) that would support the conclusion than an epidemic was underway.

Historical Antecedents
Environment and disease Use of mortality counts Use of natural experiments Identification of specific agents of disease 20

The Environment Hippocrates wrote On Airs, Waters, and Places in 400 BC. He suggested that disease might be associated with the physical environment. This represented a movement away from supernatural explanations of disease causation. 22

Use of Mortality Counts
John Graunt, in 1662, published Natural and Political Observations Made upon the Bills of Mortality. 23

John Graunt’s Contributions
Recorded seasonal variations in births and deaths. Showed excess male over female differences in mortality. Known as the “Columbus” of biostatistics.

Use of Natural Experiments
John Snow was an English physician and anesthesiologist. He investigated a cholera outbreak that occurred during the mid-19th century in Broad Street, Golden Square, London. 24

Snow’s Contributions Linked the cholera epidemic to contaminated water supplies. Used a spot map of cases and tabulation of fatal attacks and deaths.

Snow’s Natural Experiment
Two different water companies supplied water from the Thames River to houses in the same area. The Lambeth Company moved its source of water to a less polluted portion of the river. Snow noted that during the next cholera outbreak those served by the Lambeth Company had fewer cases of cholera.

Natural Experiment Definition: The epidemiologist does not manipulate a risk factor but rather observes the changes in an outcome as the result of a naturally occurring situation.

Contemporary Natural Experiments
Currently, natural experiments may be the result of legislation, policy changes or environmental interventions.

Examples of Contemporary Natural Experiments
Seat Belt Law--Did seat belt use reduce fatalities from motor vehicle accidents? Tobacco Tax--Did the increase in cigarette price decrease the sale of cigarettes? Helmet Law--Did requiring the use of helmets by motorcyclists reduce the number of head injuries sustained?

William Farr Appointed compiler of abstracts in England, 1839.
Provided foundation for classification of diseases (ICD system). Examined linkage between mortality rates and population density.

Koch's Postulates Microorganism must be observed in every case of the disease. Microorganism must be isolated and grown in pure culture. Pure culture must, when inoculated into a susceptible animal, reproduce the disease. Microorganism must be observed in, and recovered from, diseased animal. 28

Other Historical Developments
Alexander Langmuir established CDC’s Epidemiologic Intelligence Service. Wade Hampton Frost was the first professor of epidemiology in the U.S. Joseph Goldberger discovered the cure for pellagra.

Recent Applications of Epidemiology
Framingham Heart Study (since 1949) investigates coronary heart disease risk factors. Smoking and lung cancer; e.g., Doll and Peto’s study of British doctors’ smoking. AIDS, chemical spills, breast cancer screening, secondhand smoke. 30

Additional Applications of Epidemiology
Infectious diseases Environmental health Chronic diseases Lifestyle and health promotion Psychiatric and social epidemiology Molecular and genetic epidemiology 31

Practical Applications of Epidemiology
Chapter 2 Practical Applications of Epidemiology

Seven Uses of Epidemiology
To study the history of the health of populations. To diagnose the health of the community. To study the working of health services-operations research. To estimate the individual risks of disease and other conditions.

Uses, continued... To identify syndromes.
To complete the clinical picture of chronic diseases. To search for causes of health and disease.

Historical Use of Epidemiology
Refers to the study of past and future trends in health and illness. Secular trends--changes in disease frequency over time.

Examples of Trends Chronic diseases have replaced acute infectious diseases as the major causes of morbidity and mortality. Leading causes of U.S. deaths are heart disease, cancer, and stroke.

Factors Affecting Reliability of Observed Changes
Lack of comparability over time due to altered diagnostic criteria. Aging of the general population. Changes in the fatal course of the condition.

Four Trends in Disorders
Disappearing Residual Persisting New epidemic

Disappearing Disorders
This category refers to conditions that were once common but are no longer present in epidemic form; an example is smallpox.

Residual Disorders Conditions for which the key contributing factors are largely known. Methods of control not implemented effectively. Examples: STDs, alcohol abuse, tobacco use.

Persisting Disorders Diseases for which there is no effective method of prevention or no known cure. Examples: certain types of cancer.

New Epidemic Disorders
Diseases that are increasing in frequency. Examples: lung cancer, HIV.

Predictions About the Future
About 20 percent of the U.S. population in 2030 will be age 65 and older. The need for health- and aging-related services will grow.

Population Dynamics Three factors that affect the size of populations are births, deaths, and migration. When these factors do not contribute to net increases or decreases, the population is in equilibrium.

Population Terms Fixed population--adds no new members and, as a result, decreases in size due to deaths only. Dynamic population--adds new members through migration and births or loses members through emigration and deaths.

Demographic Transition
Shift from high birth and death rates found in agrarian societies to lower birth and death rates found in developed countries.

Steady Population A population is in steady state when the number of members exiting equals the number entering.

Epidemiology and the Health of the Community
Provides a key to the types of problems requiring attention. Determines the need for specific health services.

Demographic and Social Variables
Age and sex distribution Socioeconomic status Family structure Racial, ethnic, and religious composition

Variables Related to Community Infrastructure
Availability of social and health services Quality of housing stock Social stability (residential mobility)

Health-Related Outcome Variables
Homicide and suicide rates Infant mortality rate Selected mortality rates Drug and alcohol abuse rates Teen pregnancy rates Birth rate

Healthy People 2010, Goal 2 “ To eliminate health disparities among segments of the population, including differences that occur by gender, race, or ethnicity, . . .”

Epidemiology and Policy Evaluation
Using epidemiologic methodologies to evaluate public health policies Examples: tobacco control policies, drug treatment systems, food sold to schoolchildren

Operations Research (OR)
The study of the placement and optimum utilization of health services in a community.

Epidemiology and OR Methods for selecting target populations
Data analysis techniques Research designs Measurement procedures

Program Evaluation Uses epidemiologic tools to determine how well a health program meets certain stated goals.

Examples of OR Coordination of programs for the developmentally disabled Studies of health care utilization Minority access to health insurance

Epidemiology and Disease Etiology
Applications include: Search for causes Individual risks Specific clinical concerns

Modern Concepts of Causality
Five criteria for causality (source: 1964 Surgeon General’s Report): Strength of association Time sequence Consistency upon repetition Specificity Coherence of explanation

Further Consideration of Causality
Sir Austin Bradford Hill expanded the list of criteria to include: Biologic gradient Plausibility Experiment Analogy

Risk Factors Due to the uncertainty of “causal” factors the term risk factor is used. Definition: exposure that is associated with a disease. Example of a risk factor: smoking.

Three Criteria for Risk Factors
The frequency of the disease varies by category or value of the factor, e.g., light smokers vs. heavy smokers. The risk factor precedes onset of the disease. The observation must not be due to error.

Etiologic Study Designs
Case control Cohort

Case Control Design A type of design that compares persons who have a disease (cases) with those who are free from the disease (controls). This design explores whether differences between cases and controls result from exposures to risk factors.

Cohort Design A group of people free from a disease is assembled according to a variety of exposures. The group (cohort) is followed over a period of time for development of disease.

How Results Impact Clinical Decisions
The following considerations determine a study’s influence: Criteria of causality Relevance to each patient Size of the risk Public health implications Individual vs. population

Natural History of Disease
Prepathogenesis--before agent reacts with host. Pathogenesis--after agent reacts with host. Later stages include development of active signs and symptoms. Clinical end points are: recovery, disability, or death.

Primary Prevention Occurs during prepathogenesis phase.
Designed to reduce the occurrence of disease. Examples are education and immunization.

Secondary Prevention Occurs during pathogenesis phase.
Designed to reduce the progress of disease. Examples are screening programs for cancer and diabetes.

Tertiary Prevention Designed to limit disability from disease.
Also directed at restoring optimal functioning. An example is physical therapy for stroke patients.

Measures of Morbidity and Mortality Used in Epidemiology
Chapter 3 Measures of Morbidity and Mortality Used in Epidemiology

Copyright 2004 Jones and Bartlett Publishers
Learning Objectives Define and distinguish among proportions, rates, and ratios Explain the term population at risk Identify and calculate commonly used rates for morbidity, mortality, and natality State the meanings and applications of incidence rates and prevalence Copyright 2004 Jones and Bartlett Publishers

Learning Objectives (cont’d)
Discuss limitations of crude rates and alternative measures for crude rates Apply direct and indirect methods to adjust rates List situations where direct and indirect adjustment should be used Copyright 2004 Jones and Bartlett Publishers

Count The simplest and most frequently performed quantitative measure in epidemiology. Refers to the number of cases of a disease or other health phenomenon being studied. Significant for rare diseases or symptom presentations (e.g., case of Ebola virus). Copyright 2004 Jones and Bartlett Publishers

Definition of Proportion
A measure that states a count relative to the size of the group. A ratio in which the numerator is part of the denominator. May be expressed as a percentage. Copyright 2004 Jones and Bartlett Publishers

Uses of Proportions Can demonstrate the magnitude of a problem. Example: 10 dormitory students develop hepatitis. How important is this problem? If only 20 students live in the dorm, 50% are ill. If 500 students live in the dorm, 2% are ill. Copyright 2004 Jones and Bartlett Publishers

Example of a Proportion
Calculate the proportion of African-American male deaths among African-American and white males aged 5 to 14 years. A B Total (A + B) Number of deaths among Total African-American males white males 1,150 3,810 4,960 Proportion = A/(A + B) x 100 = (1,150/4,960) x100 = 23.2% Copyright 2004 Jones and Bartlett Publishers

Ratio Fraction (consists of both numerator and denominator) No specified relationship between numerator and denominator Number of male cases Number of female cases 19:1 male to female = Copyright 2004 Jones and Bartlett Publishers

Rate Definition: a ratio that consists of a numerator and a denominator and in which time forms part of the denominator. Contains the following elements: disease frequency unit size of population time period during which an event occurs Copyright 2004 Jones and Bartlett Publishers

Example of Rate Number of deaths in a given year Reference Population (during midpoint of the year) Crude Death Rate = x 100,000 Example: Number of deaths in the United States during 1990 = 2,148,463 Population of the U.S. as of June 30, 1990 = 248,709,873 2,148,463 248,709,873 Crude Death Rate = = per 100,000 Copyright 2004 Jones and Bartlett Publishers

Definition of Prevalence
The number of existing cases of a disease or health condition in a population at some designated time. Copyright 2004 Jones and Bartlett Publishers

Interpretation of Prevalence
Provides an indication of the extent of a health problem. Example 1: prevalence of diarrhea in a children’s camp on July 13 was 33% (point prevalence). Example 2: prevalence of cancer in women during a specified time period (period prevalence) Copyright 2004 Jones and Bartlett Publishers

Uses of Prevalence Describing the burden of a health problem in a population. Estimating the frequency of an exposure. Determining allocation of health resources such as facilities and personnel. Copyright 2004 Jones and Bartlett Publishers

Point Prevalence Point Prevalence = Number of persons ill Total number in the group at point in time Example: Total number of smokers in the group = ,234 Total number in the group ,837 or 14.9% = per 1,000 Copyright 2004 Jones and Bartlett Publishers

Period Prevalence Period Prevalence = during a time period Number of persons ill Average population Example: Persons ever diagnosed with cancer = ,293 Average Population ,837 = 5.5% Copyright 2004 Jones and Bartlett Publishers

Incidence Rate (Cumulative Incidence)
Describes the rate of development of a disease in a group over a certain time period. Contains three elements: Numerator = the number of new cases. Denominator = the population at risk. Time = the period during which the cases occur. Copyright 2004 Jones and Bartlett Publishers

Applications of Incidence Data
Helps in research on the etiology/causality of disease. Estimates the risk of developing a disease. Used to estimate the effects of exposure to a hypothesized factor of interest. Copyright 2004 Jones and Bartlett Publishers

Incidence Rate Calculation
Number of new cases over a time period x Total population at risk multiplier Number of new cases = 1,085 Population at risk = 37,105 1,085 37,105 = cases per 100,000 women per year Incidence Rate = = /8 = x 100,000 Copyright 2004 Jones and Bartlett Publishers

Attack Rate Alternative form of incidence rate. Used for diseases observed in a population for a short time period. Example: Salmonella gastroenteritis outbreak Formula: Ill___ Ill + Well AR = x 100 (during a time period) Copyright 2004 Jones and Bartlett Publishers

Formulas for Incidence Density
Number of new cases during the time period Total person-time of observation If period of observation is measured in years, formula becomes: Total person-years of observation Incidence Density = Copyright 2004 Jones and Bartlett Publishers

Incidence Density, example
Copyright 2004 Jones and Bartlett Publishers

Interrelationship Between Prevalence and Incidence
Interrelationship: P ID = ~ The prevalence (P) of a disease is proportional to the incidence rate (I) times the duration (D) of a disease. Copyright 2004 Jones and Bartlett Publishers

Prevalence and Incidence (cont’d)
If duration of disease is short and incidence is high, prevalence becomes similar to incidence. Short duration--cases recover rapidly or are fatal Example: common cold Copyright 2004 Jones and Bartlett Publishers

Prevalence and Incidence (cont’d)
If duration of disease is long and incidence is low, prevalence increases greatly relative to incidence. Example: many chronic diseases Copyright 2004 Jones and Bartlett Publishers

Crude Rates, Measures of Natality
Crude birth rate Fertility rate Infant mortality rate Fetal death rate Neonatal mortality rate Postneonatal mortality rate Perinatal mortality rate Maternal mortality rate Copyright 2004 Jones and Bartlett Publishers

Crude Birth Rate Used to project population changes; it is affected by the number and age composition of women of childbearing age Number of live births within a given period Crude Birth Rate = X 1,000 population Population size at the middle of that period Sample calculation: 4,111,000 babies were born in the U.S. during 1991, when the U.S. population was 252,688,000. The birth rate was 4,111,000/252,688,000 = 16.3 per 1,000. Copyright 2004 Jones and Bartlett Publishers

General Fertility Rate
Used for comparisons of fertility among age, racial, and socioeconomic groups. # of live births within a year General fertility rate 1,000 women aged 15-44 = X # of women aged yrs. during the midpoint of the year Copyright 2004 Jones and Bartlett Publishers

Infant Mortality Rate Used for international comparisons; a high rate indicates unmet health needs and poor environmental conditions. Number of infant deaths among infants aged days during the year 1,000 live births Infant Mortality = X Number of live births during the year Copyright 2004 Jones and Bartlett Publishers

Fetal Death Rate Used to estimate the risk of death of the fetus associated with the stages of gestation. Fetal Death Rate (per 1,000 live births plus fetal deaths) = Number of fetal deaths after 20 weeks or more gestation Number of live births + number of fetal deaths after 20 weeks or more gestation X 1,000 Late fetal death rate (per 1,000 live births plus late fetal deaths) = Number of fetal deaths after 28 weeks or more gestation Number of live births + number of fetal deaths after 28 weeks or more gestation X 1,000 Copyright 2004 Jones and Bartlett Publishers

Fetal Death Ratio Provides a measure of fetal wastage (loss) relative to the number of live births. Number of fetal deaths after 20 weeks or more gestation Number of live births X 1,000 (during a year) Fetal Death Ratio = Copyright 2004 Jones and Bartlett Publishers

Neonatal Mortality Rate
Reflects events happening after birth, primarily: congenital malformations prematurity (birth before gestation week 28) low birth weight (birth weight less than 2,500 g) Copyright 2004 Jones and Bartlett Publishers

Neonatal Mortality Rate Formula
Number of infant deaths under 28 days of age Number of live births X 1,000 live births (during a year) Copyright 2004 Jones and Bartlett Publishers

Postneonatal Mortality Rate
Reflects environmental events, control of infectious diseases, and improvement in nutrition. Postneonatal Mortality Rate = Number of infant deaths from 28 days to 365 days after birth Number of live births - neonatal deaths X 1,000 live births Copyright 2004 Jones and Bartlett Publishers

Perinatal Mortality Rate
Reflects environmental events that occur during pregnancy and after birth; it combines mortality during the prenatal and postnatal periods. Perinatal Mortality Rate = Number of late fetal deaths after 28 weeks or more gestation plus infant deaths within 7 days of birth X 1,000 live births and fetal deaths Number of live births + number of late fetal deaths Copyright 2004 Jones and Bartlett Publishers

Perinatal Mortality Ratio
Number of late fetal deaths after 28 weeks or more gestation plus infant deaths within 7 days of birth Perinatal Mortality Ratio = X 1,000 live births Number of live births Copyright 2004 Jones and Bartlett Publishers

Maternal Mortality Rate
Reflects health care access and socioeconomic factors; it includes maternal deaths resulting from causes associated with pregnancy and puerperium (during and after childbirth). Maternal Mortality Rate (per 100,000 live births, includes multiple births) = Number of deaths assigned to causes related to childbirth Number of live births X 100,000 live births (during a year) Copyright 2004 Jones and Bartlett Publishers

Crude Rates Use crude rates with caution when comparing disease frequencies between populations. Observed differences in crude rates may be the result of systematic factors (e.g., sex or age distributions) within the population rather than true variation in rates. Copyright 2004 Jones and Bartlett Publishers

Cause-Specific Rate Cause-Specific Rate = Mortality (or frequency of a given disease) X 100,000 Population size at midpoint of time period Example: Cause-specific mortality rate due to HIV in 1996 = 22,795/83,761,000 = 27.2 per 100,000 Copyright 2004 Jones and Bartlett Publishers

Proportional Mortality Ratio (PMR)
Mortality due to a specific cause during a time period X 100 Mortality due to all causes during the same time period Example: PMR (%) for HIV among the 25- to 44-year-old group = 22,795/148,904 = 15.3% Indicates relative importance of a specific cause of death; not a measure of the risk of dying of a particular cause. Copyright 2004 Jones and Bartlett Publishers

Age-Specific Rate The number of cases per age group of population (during a specified time period). Example: Number of deaths among those aged 5-14 years Number of persons who are 5-14 years (during time period) X 100,000 Sample calculation: In the U.S. during 1991, there were 1,106 deaths due to malignant neoplasms among the age group 5 to 14 years, and there were 35,904,000 persons in the same age group. The age-specific malignant neoplasm death rate in this age group is (1,106/35,904,000) = 3.1 per 100,000. Copyright 2004 Jones and Bartlett Publishers

Method for Calculation of Age-Specific Death Rates

Adjusted Rates Summary measures of the rate of morbidity and mortality in a population in which statistical procedures have been applied to remove the effect of differences in composition of various populations. Copyright 2004 Jones and Bartlett Publishers

Direct Method Direct method may be used if age-specific death rates in a population to be standardized are known and a suitable standard population is available. Copyright 2004 Jones and Bartlett Publishers

Indirect Method Indirect method may be used if age-specific death rates of the population for standardization are unknown or unstable, for example, because the population is small. Copyright 2004 Jones and Bartlett Publishers

Direct Method for Adjustment of Death Rates

New Standard Population
Year 2000 population Replaces the standard based on 1940 population. Results in age-adjusted death rates that are much larger. Affects trends in age-adjusted rates for certain causes of death. Narrows race differentials in age-adjusted death rates. Reduces the three different standards into one acceptable standard. Copyright 2004 Jones and Bartlett Publishers

Standardized Mortality Ratio (SMR)
Observed deaths Expected deaths x 100 Sample calculation: The number of observed deaths due to heart disease is 600 in a certain county during year The expected number of deaths is 1,000. The SMR = (600/1,000 x 100) = 60% (0.6). Copyright 2004 Jones and Bartlett Publishers

Interpretation of SMR If the observed and expected numbers are the same, the SMR would be 1.0, indicating that observed mortality is not unusual. An SMR of 2.0 means that the death rate in the study population is two times greater than expected. Copyright 2004 Jones and Bartlett Publishers

Indirect Age Adjustment (cont’d)
From previous table, SMR is (502/423) X 100 = 118.7% Copyright 2004 Jones and Bartlett Publishers

Descriptive vs. Analytic Epidemiology
Descriptive studies--used to identify a health problem that may exist. Characterize the amount and distribution of disease. Analytic studies--follow descriptive studies, and are used to identify the cause of the health problem. Copyright 2004 Jones and Bartlett Publishers 2

Objectives of Descriptive Epidemiology
To evaluate and compare trends in health and disease. To provide a basis for planning, provision, and evaluation of health services. To identify problems for analytic studies (creation of hypothesis). Copyright 2004 Jones and Bartlett Publishers 3

Descriptive Studies and Epidemiologic Hypotheses
Hypotheses--theories tested by gathering facts that lead to their acceptance or rejection. Three types: Positive declaration (research hypothesis) Negative declaration (null hypothesis) Implicit question Copyright 2004 Jones and Bartlett Publishers 4

Mill’s Canons of Inductive Reasoning
The method of difference--all the factors in two or more places are the same except for a single factor. The method of agreement--a single factor is common to a variety of settings. Example: air pollution. Copyright 2004 Jones and Bartlett Publishers 5

Mill’s Canons (cont’d)
The method of concomitant variation--the frequency of disease varies according to the potency of a factor. The method of residues--involves subtracting potential causal factors to determine which factor(s) has the greatest impact. Copyright 2004 Jones and Bartlett Publishers 6

Method of Analogy The mode of transmission and symptoms of a disease of unknown etiology bear a pattern similar to that of a known disease. This information suggests similar etiologies for both diseases. Copyright 2004 Jones and Bartlett Publishers

Categories of Descriptive Epidemiology
Case reports (counts)--simplest category. Case series--summarize characteristics of patients from major clinical settings. Cross-sectional studies--surveys of the population to estimate the prevalence of a disease or exposure. Copyright 2004 Jones and Bartlett Publishers 7

Characteristics of Persons
Age Sex Marital Status Race and ethnicity Nativity and migration Religion Socioeconomic status Copyright 2004 Jones and Bartlett Publishers

Age One of the most important factors to consider when describing the occurrence of any disease or illness. Age-specific distributions can be linear (e.g., cancer), or multimodal (e.g., tuberculosis). Age-specific incidence rates among elderly often inaccurate. Copyright 2004 Jones and Bartlett Publishers 8

Age Effects on Mortality
Biologic clock phenomenon--waning of the immune system may result in increased susceptibility to disease, or aging may trigger appearance of conditions believed to have genetic basis. Example: Alzheimer’s disease. Copyright 2004 Jones and Bartlett Publishers 9

Age Effects (cont’d) Latency period—Age effects on mortality may reflect the long latency period between environmental exposures and subsequent development of disease. Copyright 2004 Jones and Bartlett Publishers

Sex--Males Mortality rate higher for men than for women. May be due to social factors. May have biological basis. Example: With risk status being equal, men still have higher mortality from CHD. Copyright 2004 Jones and Bartlett Publishers 10

Marital Status In general, married people have lower rates of morbidity and mortality. Examples: chronic and infectious diseases, suicides, and accidents. Copyright 2004 Jones and Bartlett Publishers 11

Marital Status (cont’d)
Marriage may operate as a protective or selective factor. Protective: may provide an environment conducive to health. Selective: people who marry may be healthier to begin with. Copyright 2004 Jones and Bartlett Publishers

Measurement of Race Census 2000 changed the race category by allowing respondents to choose one or more race categories. Census 2000 used five categories of race (Exhibit 4-1). Copyright 2004 Jones and Bartlett Publishers

Race/Ethnicity Categories Discussed in Chapter 4
African American American Indian Asian Hispanic/Latino Copyright 2004 Jones and Bartlett Publishers

African Americans In a study of differential mortality in U.S., had the highest rate of mortality of all groups studied. Higher blood pressure levels Possible influence of stress or diet. Higher rates of hypertensive heart disease. Copyright 2004 Jones and Bartlett Publishers 12

American Indians For Pima Indians: Age- and sex-adjusted mortality rate many times that for all races in U.S. for: accidents, cirrhosis, homicide, suicide, and diabetes. Infectious disease is the 10th leading cause of death. For males ages 25 to 34, the death rate is 6.6 times that for all races in U.S. Copyright 2004 Jones and Bartlett Publishers 13

Asians--Japanese Comparatively lower mortality rates. Lower rates of CHD and cancer. Low CHD rates attributed to low-fat diet and institutionalized stress-reducing strategies. Copyright 2004 Jones and Bartlett Publishers 14

Acculturation Defined as modifications that individuals or groups undergo when they come in contact with another country. Provide evidence of the influence of environmental and behavioral factors on chronic disease. Example: Japanese migrants experience a shift in rates of chronic disease toward those of the host country. Copyright 2004 Jones and Bartlett Publishers 15

Hispanics/Latinos Hispanic Health and Nutrition Examination Survey (HHANES). Examined health and nutrition status of major Hispanic/Latino populations in the U.S. San Antonio Heart Study Found high rates of obesity and diabetes among Mexican Americans. Copyright 2004 Jones and Bartlett Publishers 16

Nativity and Migration
Nativity--Place of origin of the individual. Categories are foreign born and native born. Nativity and migration are related. Copyright 2004 Jones and Bartlett Publishers 17

Impact of Migration Importation of “Third World” disease by immigrants from developing countries. Programmatic needs resulting from migration: Specialized screening programs (tuberculosis and nutrition). Familiarization with formerly uncommon (in U.S.) tropical diseases. Copyright 2004 Jones and Bartlett Publishers

Healthy Migrant Effect
Observation that healthier, younger persons usually form the majority of migrants. Often difficult to separate environmental influences in the host country from selective factors operative among those who choose to migrate. Copyright 2004 Jones and Bartlett Publishers

Religion Certain religions prescribe lifestyles that may influence rates of morbidity and mortality. Example: Seventh Day Adventists Follow vegetarian diet and abstain from alcohol and tobacco use. Have lower rates of CHD, reduced cancer risk, and lower blood pressure. Similar findings for Mormons. Copyright 2004 Jones and Bartlett Publishers 18

Socioeconomic Status Low social class is related to excess mortality, morbidity, and disability rates. Factors include: Poor housing Crowded conditions Racial disadvantage Low income Poor education Unemployment Copyright 2004 Jones and Bartlett Publishers 19

Measurement of Social Class
Variables include: Prestige of occupation or social position Educational attainment Income Combined indices of two or more of the above variables Copyright 2004 Jones and Bartlett Publishers 20

Hollingshead and Redlich
Studied association of socioeconomic status and mental illness. Classified New Haven, Connecticut, into five social classes based on occupational prestige, education, and address. Copyright 2004 Jones and Bartlett Publishers 23

Hollingshead and Redlich Findings
Strong inverse association between social class and likelihood of being a mental patient under treatment. As social class increased, severity of mental illness decreased. Type of treatment varied by social class. Copyright 2004 Jones and Bartlett Publishers 24

Mental Health and Social Class
In the U.S., the highest incidence of severe mental illness occurs among the lowest social classes. Copyright 2004 Jones and Bartlett Publishers

Mental Health and Social Class: Two Hypotheses
Social causation explanation (breeder hypothesis)--conditions associated with lower social class produce mental illness. Downward drift hypothesis—Persons with severe mental disorders move to impoverished areas. Copyright 2004 Jones and Bartlett Publishers 21

Other Correlates of Low Social Class
Higher rate of infectious disease. Higher infant mortality rate and overall mortality rates. Lower life expectancy. Larger proportion of cancers with poor prognosis. May be due to delay in seeking health care. Copyright 2004 Jones and Bartlett Publishers 22

Characteristics of Place
Types of place comparisons: International Geographic (within-country) variations Urban/rural differences Localized occurrence of disease Copyright 2004 Jones and Bartlett Publishers 25

International Comparisons of Disease Frequency
World Health Organization (WHO) tracks international variations in rates of disease. Infectious diseases account for 44% of deaths in less developed nations (4% in developed nations). Variation attributable to climate, cultural factors and dietary habits. Copyright 2004 Jones and Bartlett Publishers 26

Within-Country Variations in Rates of Disease
Due to variations in climate, geology, latitude, pollution, and ethnic and racial concentrations. In U.S., comparisons can be made by region, state, and/or county. Examples include: higher rates of leukemia in Midwest; state by state variations in intestinal parasites. Copyright 2004 Jones and Bartlett Publishers 27

Urban/Rural Differences in Disease Rates
Urban diseases and mortality are associated with crowding, pollution, and poverty. Example: lead poisoning in inner cities. Copyright 2004 Jones and Bartlett Publishers 28

Standard Metropolitan Statistical Areas (SMSAs)
Established by the U.S. Bureau of the Census to make regional and urban/rural comparisons in disease rates. Copyright 2004 Jones and Bartlett Publishers

Localized Place Comparisons
Disease patterns are due to unique environmental or social conditions found in particular areas of interest. Examples include: Fluorosis: associated with naturally occurring fluoride deposits in water. Goiter: iodine deficiency formerly found in land-locked areas of U.S. Copyright 2004 Jones and Bartlett Publishers 29

Geographic Information Systems (GIS)
A method to provide a spatial perspective on the geographic distribution of health conditions. A GIS produces a choroplath map that shows variations in disease rates by different degrees of shading. Copyright 2004 Jones and Bartlett Publishers

Reasons for Place Variation in Disease
Gene/environment interaction Examples: sickle-cell gene; Tay-Sachs disease. Influence of climate Examples: yaws, Hansen’s disease Environmental factors Example: chemical agents linked to cancer Copyright 2004 Jones and Bartlett Publishers 30

Characteristics of Time
Cyclic fluctuations Point epidemics Secular time trends Clustering Temporal Spatial Copyright 2004 Jones and Bartlett Publishers 31

Cyclic Fluctuations Periodic changes in the frequency of diseases and health conditions over time. Related to changes in lifestyle of the host, seasonal climatic changes, and virulence of the infectious agent. Examples: higher heart disease mortality in winter; more accidents in summer. Copyright 2004 Jones and Bartlett Publishers

Point Epidemics The response of a group of people circumscribed in place and time to a common source of infection, contamination, or other etiologic factor to which they were exposed almost simultaneously. Examples: foodborne illness; responses to toxic substances; infectious disease. Copyright 2004 Jones and Bartlett Publishers 32

Secular Time Trends Refer to gradual changes in the frequency of a disease over long time periods. Example is the decline of heart disease mortality in the U.S. May reflect impact of public health programs, dietary improvements, better treatment, or unknown factors. Copyright 2004 Jones and Bartlett Publishers 33

Clustering Case clustering--refers to an unusual aggregation of health events grouped together in space and time. Temporal clustering: e.g., post-vaccination reactions, postpartum depression. Spatial clustering: concentration of disease in a specific geographic area, e.g., Hodgkin’s disease. Copyright 2004 Jones and Bartlett Publishers 35

Chapter 5 Sources of Data for Use in Epidemiology

Criteria for the Quality and Utility of Epidemiologic Data
Nature of the data Availability of the data Completeness of population coverage Representativeness (external validity) Thoroughness Value and limitations Copyright 2004 Jones and Bartlett Publishers 2

Nature of the Data Refers to the source of data, e.g., vital statistics, case registries, physicians’ records, surveys of the general population, or hospital and clinic cases. Will affect the types of statistical analyses and inferences that are possible. Copyright 2004 Jones and Bartlett Publishers 3

Availability of the Data
Refers to investigator’s access to data. For example, medical records and other data with personal identifiers may not be used without patients’ consent. Copyright 2004 Jones and Bartlett Publishers 4

Representativeness and Thoroughness
Representativeness (external validity)--generalizability of findings to the population from which the data have been taken. Thoroughness--the extent to which all cases of a health phenomenon have been identified. Copyright 2004 Jones and Bartlett Publishers 5

Value and Limitations The utility of the data for various types of epidemiologic research. Factors inherent in the data may limit their usefulness. Incomplete diagnostic information. Case duplication. Copyright 2004 Jones and Bartlett Publishers 6

Computerized Bibliographic Databases
Facts related to the distribution of diseases can be obtained through such sources as: Index Medicus, Psychological Abstracts, Sociological Abstracts, Education Index. On-line databases include Medline, Toxline, and DIALOG. Internet, including World Wide Web. Copyright 2004 Jones and Bartlett Publishers 7

Confidentiality Privacy Act of 1974 Prohibits the release of confidential data without the consent of the individual. Freedom of Information Act Mandates the release of government information to the public, except for personal and medical files. The Public Health Service Act Protects confidentiality of information collected by some federal agencies, e.g., NCHS. Copyright 2004 Jones and Bartlett Publishers 8

Data Sharing Refers to the voluntary release of information by one investigator or institution to another for the purpose of scientific research. Key issue is the primary investigator’s potential loss of control over information. Copyright 2004 Jones and Bartlett Publishers 9

Record Linkage Joining data from two or more sources, e.g., employment records and mortality data. Applications include genetic research, planning of health services, and chronic disease tracking. Copyright 2004 Jones and Bartlett Publishers 10

Statistics Derived from the Vital Registration System
Mortality statistics Birth statistics: certificates of birth and fetal death. Copyright 2004 Jones and Bartlett Publishers 11

Mortality Statistics Mortality data are nearly complete, since most deaths in the U.S. and other developed countries are unlikely to be unreported. Death certificates include demographic information about the deceased and cause of death (immediate cause and contributing factors). Copyright 2004 Jones and Bartlett Publishers 12

Limitations of Mortality Data
Certification of cause of death. For example, in an elderly person with chronic illness, exact cause of death may be unclear. Lack of standardization of diagnostic criteria. Stigma associated with certain diseases, e.g., AIDS, may lead to inaccurate reporting. Copyright 2004 Jones and Bartlett Publishers 13

Limitations of Mortality Data (Cont’d)
Errors in coding by nosologist. Changes in coding. Revisions in the (ICD) International Classification of Disease. Sudden increases or decreases in a particular cause of death may be due to changes in coding. Copyright 2004 Jones and Bartlett Publishers 14

Birth Statistics: Certificates of Birth and of Fetal Death
Birth certificate includes information that may affect the neonate, such as congenital malformations, birth weight, and length of gestation. Sources of unreliability: Mothers’ recall of events during pregnancy may be inaccurate. Conditions which affect neonate may not be present at birth. Copyright 2004 Jones and Bartlett Publishers 15

Birth Statistics (Cont’d)
Varying state requirements for fetal death certificates. Both types of certificates have been used in studies of environmental influences upon congenital malformations. Both provide nearly complete data. Copyright 2004 Jones and Bartlett Publishers 16

Reportable Disease Statistics
Federal and state statutes require health care providers to report those cases of diseases classified as reportable and notifiable. Include infectious and communicable diseases that endanger a population, e.g., STDs, measles, foodborne illness. Copyright 2004 Jones and Bartlett Publishers 17

Limitations of Reportable Disease Statistics
Possible incompleteness of population coverage. For example, asymptomatic persons would not seek treatment. Failure of physician to fill out required forms. Unwillingness to report cases that carry a social stigma. Copyright 2004 Jones and Bartlett Publishers 18

Screening Surveys Conducted on an ad-hoc basis to identify individuals who may have infectious or chronic diseases. Examples: breast cancer screenings, health fairs. Clientele are highly selected. Individuals who participate are concerned about the particular health issue. Copyright 2004 Jones and Bartlett Publishers 19

Multiphasic Screening Programs
Ongoing screening programs often are carried out at worksites. Data can be useful for research on occupational health problems. Biases of data due to worker attrition and turnover. Data may not contain etiologic information. Copyright 2004 Jones and Bartlett Publishers 20

Disease Registries Registry--a centralized database for collection of data about a disease. Coding algorithms are used to maintain patient confidentiality. Applications of registries: Patient tracking Identification of trends in rates of disease Case control studies Example: SEER program Copyright 2004 Jones and Bartlett Publishers 21

Surveillance, Epidemiology, and End Results (SEER) Program
Conducted by the National Cancer Institute (NCI). Collects cancer data from different cancer registries across the U.S. Provides information about trends in cancer incidence, mortality, and survival. Copyright 2004 Jones and Bartlett Publishers 22

Morbidity Surveys of the General Population
Collect data on the health status of a population group. Obtain more comprehensive information than would be available from routinely collected data. Example: National Health Survey Copyright 2004 Jones and Bartlett Publishers 23

National Health Survey
Authorized under the National Health Survey Act of 1956 to obtain information about the health of the U.S. population. Conducted by the NCHS; consists of three programs: National Health Interview Survey (HIS, a household health interview survey) Health Examination Survey (HES) Surveys of health resources Copyright 2004 Jones and Bartlett Publishers 24

Household Interview Survey (HIS)
General household health survey of the U.S. civilian noninstitutionalized population. Studies a comprehensive range of conditions such as diseases, injuries, disabilities, and impairments. Copyright 2004 Jones and Bartlett Publishers 25

Health Examination Survey (HES)
Provides direct information about morbidity through examinations, measurements, and clinical tests. Identifies conditions previously unreported or undiagnosed. Provides information not previously available for a defined population. Now known as the Health and Nutrition Examination Survey (HANES). Copyright 2004 Jones and Bartlett Publishers 26

Insurance Data Sources include: Social Security--provides data on disability benefits and Medicare. Health insurance--provides data on those who receive care through a prepaid medical program. Life insurance--provides information on causes of mortality; also provides results of physical examinations. Copyright 2004 Jones and Bartlett Publishers 27

Limitations of Insurance Data
Data may not be representative of entire population, as the uninsured are excluded. Copyright 2004 Jones and Bartlett Publishers

Hospital Data Consists of both inpatient and outpatient data. Deficiencies of data: Not representative of any specific population. Different information collected on each patient. Settings may differ according to social class of patients; e.g., specialized clinics, emergency rooms. Copyright 2004 Jones and Bartlett Publishers 28

Diseases Treated in Special Clinics and Hospitals
Data cannot be generalized because patients are a highly selected group. Case control studies can be done with unusual and rare diseases. However, it is not possible to determine incidence and prevalence rates without knowing the size of the denominator. Copyright 2004 Jones and Bartlett Publishers 29

Data from Physicians’ Practices
Limited application due to: Confidentiality of patient data. Highly selected group of patients. Lack of standardization of information collected. Useful for the purposes of: Verification of self-reports. Source of exposure data. Copyright 2004 Jones and Bartlett Publishers 30

Absenteeism Data Records of absenteeism from work or school. Possible deficiencies: Data omit people who neither work nor attend school. Not all people who are ill take time off. Those absent are not necessarily ill. Useful for the study of rapidly spreading conditions. Copyright 2004 Jones and Bartlett Publishers 31

School Health Programs
Provide information about immunizations, physical exams, and self-reports of illness. Have been used in studies of intelligence, mental retardation, and disease etiology. Paffenbarger, et al. used information from health records of college students to track causes of chronic diseases. Copyright 2004 Jones and Bartlett Publishers 32

Morbidity Data from the Armed Forces
Reports from physicals, hospitalizations, and selective service examinations. Data have been used for: Studies of disease etiology. Study of twins serving in Korean War or WWII to determine influence of “nature and nurture” on cause of disease. Studies investigating genetic factors in obesity. Copyright 2004 Jones and Bartlett Publishers 33

Other Data Sources Relevant to Epidemiologic Studies
U.S. Bureau of the Census publications: Statistical Abstract of the U.S. County and City Data Book Decennial Censuses of Population and Housing Historical Statistics of the U.S., Colonial Time to 1957 Copyright 2004 Jones and Bartlett Publishers 34

U.S. Bureau of the Census Provides information on the general, social, and economic characteristics of the U.S. population. U.S. Census administered every 10 years. Attempts to account for every person and his or her residence. Characterizes population according to sex, age, family relationships, and other demographic variables. Copyright 2004 Jones and Bartlett Publishers 37

Metropolitan Statistical Areas (MSAs)
Provide a distinction between metropolitan and nonmetropolitan areas by type of residence, industrial concentration, and population concentration. Copyright 2004 Jones and Bartlett Publishers 35

Definition of MSA To be defined as an MSA, an area must include one of the following: One city with a population of 50,000 or more. An area defined as urbanized (total MSA population of at least 100,000). Copyright 2004 Jones and Bartlett Publishers

Census Tracts Small geographic subdivisions of cities, counties, and adjacent areas. Each tract contains about 4,000 residents. Are designed to provide a degree of uniformity of population economic status and living conditions in each tract. Copyright 2004 Jones and Bartlett Publishers 36

Study Designs: Ecologic, Cross-sectional, Case- Control
Chapter 6 Study Designs: Ecologic, Cross-sectional, Case- Control

Lecture Outline Review epidemiologic concepts
A typology of study designs The cross-sectional study The ecologic study The case-control study Conclusions

What is Epidemiology? Epidemiology is concerned with the distribution and determinants of health and diseases, morbidity, injuries, disability and mortality in populations.

Review of Definitions Prevalence (point)--refers to all cases of a disease in a population of interest at a specified point in time. Incidence--refers to new cases of a disease that occur among a population at risk during a specified period of time.

How Study Designs Differ
Number of observations made Directionality of exposure Data collection methods Timing of data collection Unit of observation Availability of subjects

Observational Vs. Experimental Approaches
Manipulation of study factor Was exposure of interest controlled by investigator? Randomization of study subjects Was there use of a random process to determine exposure of study subjects?

Typology of Epidemiologic Research

Overview of Study Designs
Experimental studies Quasi-experimental studies Observational studies Descriptive studies: cross-sectional surveys Analytic studies: many ecologic studies, case-control studies, cohort studies

Ecologic Studies The unit of analysis is the group, not the individual. Correlations are obtained between exposure rates and disease rates among different groups or populations.

Types of Ecologic Studies
Ecologic comparison study—examines exposure rates and disease rates among different groups over the same time period. Ecologic trend study—examines changes in exposure and changes in disease within the same community, country, or other aggregate unit.

Example of an Ecologic Study
The association between breast cancer and dietary fat for 39 countries. High intakes of dietary fats associated with high rates of breast cancer mortality.

Additional Examples of Ecologic Studies
Childhood lead poisoning in communities in Massachusetts. Mean systolic blood pressure levels and stroke mortality rates in the Seven Countries Study.

The Ecologic Fallacy: Definition
Observations made at the group level may not represent the exposure-disease relationship at the individual level. The ecologic fallacy occurs when incorrect inferences about the individual are made from group level data.

The Ecologic Study: Example
An ecologic study finds that 70% of men have sunburned heads although 60% wore hats. The media report that wearing hats will not protect you from sunburn.

What the Individual Data Show

The Ecologic Fallacy (cont’d)
From the ecologic data, one would conclude that wearing hats affords little protection from sunburn. From the individual data, one observes that 100% of men (4) who did not wear hats were sunburned. Among men who wore hats (6), only 50% were sunburned

Ecologic Studies: Advantages and Disadvantages
Quick, simple, inexpensive Good approach for generating hypotheses when a disease is of unknown etiology Disadvantages Ecological fallacy Imprecise measurement of exposure and disease

Cross-Sectional Study
A type of prevalence study. Exposure and disease measures obtained at the individual level. Single period of observation. Exposure and disease histories collected simultaneously. Both probability and non-probability sampling used.

Cross-Sectional Study: Examples
Surveys of smokeless tobacco use among high school students. Prevalence surveys of the number of vasectomies performed. Prevalence of congenital malformations across maternal age groups.

Uses of Cross-Sectional Studies
Hypothesis generation Intervention planning Estimation of the magnitude and distribution of a health problem

Limitations of Cross-Sectional Studies
Do not provide incidence data. Cannot study low prevalence diseases. Cannot determine temporality of exposure and disease.

Overview of Case-Control Studies
In a case-control study with two groups, one group has the disease of interest (cases) and a comparable group is free from the disease (controls). The case-control study identifies possible causes of disease by finding out how the two groups differ with respect to exposure to some factor.

Characteristics of the Case-Control Study
A single point of observation. Defined by presence or absence of the outcome. Exposure is determined retrospectively. Does not directly provide incidence data.

Sources of Cases Need to define a case conceptually.
Ideally, identify and enroll all incident cases in a defined population in a specified time period. A tumor registry or vital statistics bureau may provide a complete listing of all cases. Medical facilities also may be a source of cases, but not always incident cases.

Sources of Controls Population-based controls
Patients from the same hospital as the cases Relatives of cases Friends of cases--SES control

Measures of Association

Case-Control Studies Sample Calculation
On the association between chili pepper consumption and gastric cancer risk: a case-control study conducted in Mexico City. Source: Lopez-Carillo, et al. Am J Epidemiol. 1994;139:

Sample Calculation (cont’d)

Interpretation of an Odds Ratio (OR)
OR=1 implies no association. Assuming statistical significance: OR = 2 suggests cases were twice as likely as controls to be exposed. OR<1 suggests a protective factor.

Odds Ratio (cont’d) An OR provides a good approximation of risk when:
Controls are representative of a target population. Cases are representative of all cases. The frequency of disease in the population is small.

Examples of Case-Control Studies
Green tea consumption and lung cancer Maternal anesthesia and development of fetal birth defects Passive smoking at home and risk of acute myocardial infarction

Advantages of Case-Control Studies
Tend to use smaller sample sizes than surveys or prospective studies. Quick and easy to complete. Cost effective. Useful for studies of rare diseases.

Limitations of Case-Control Studies
Provide indirect estimate of risk. Timing of exposure-disease relationship difficult to determine. Representativeness of cases and controls often unknown.

Key Points to Remember Descriptive studies: cross-sectional surveys (hypothesis generation) Analytic studies: ecologic, case-control, and cohort (hypothesis testing)

Conclusion Study designs differ in a number of key respects, including: the unit of observation the unit of analysis the timing of exposure data in relation to occurrence of disease endpoint complexity rigor amount of resources required.

Study Designs: Cohort Studies
Chapter 7 Study Designs: Cohort Studies

Learning Objectives Differentiate cohort studies from other study designs. List main characteristics, advantages, and disadvantages of cohort studies. Describe three research questions that lend themselves to cohort studies. Calculate and interpret a relative risk. Copyright 2004 Jones and Bartlett Publishers

Temporality Temporality refers to the timing of information about cause and effect. Did the information about cause and effect refer to the same point in time? Or, was the information about the cause garnered before or after the information about the effect? Copyright 2004 Jones and Bartlett Publishers

Limitations of Other Study Designs
Demonstrating temporality is a difficulty of most observational studies. Copyright 2004 Jones and Bartlett Publishers

Limitations of Other Study Designs (cont’d)
Cross-sectional and case-control study designs are based on exposure and disease information that is collected at the same time. Advantage: Efficient for generating and testing hypotheses. Disadvantage: Leads to challenges regarding interpretation of results. Copyright 2004 Jones and Bartlett Publishers

Cross-sectional studies: Present difficulties in distinguishing the exposures from the outcomes of the disease, especially if the outcome marker is a biological or physiological parameter. Copyright 2004 Jones and Bartlett Publishers

There has been no actual lapse of time between measurement of exposure and disease. None of the previous study designs is well-suited for uncommon exposures. Copyright 2004 Jones and Bartlett Publishers

What is a cohort? A cohort is defined as a population group, or subset thereof, that is followed over a period of time. The term cohort is said to originate from the Latin cohors, which referred to one of ten divisions of an ancient Roman legion. Copyright 2004 Jones and Bartlett Publishers

What is a cohort? (cont’d)
Cohort group members experience a common exposure associated with a specific setting (e.g., an occupational cohort or a school cohort) or they share a non-specific exposure associated with a general classification (e.g., a birth cohort—being born in the same year or era). Copyright 2004 Jones and Bartlett Publishers

Cohort Effect The influence of membership in a particular cohort. Example: Tobacco use in the U.S. Less than 5% of population smoked around 1900. Free cigarettes for WWI troops increased prevalence of smoking in the population. During WWI, age of onset varied greatly; then people began smoking earlier in life. One net effect: a shift in the distribution of the age of onset of lung cancer. Copyright 2004 Jones and Bartlett Publishers

Cohort Analysis The tabulation and analysis of morbidity or mortality rates in relationship to the ages of a specific group of people (cohort) identified at a particular period of time and followed as they pass through different ages during part or all of their life span. Copyright 2004 Jones and Bartlett Publishers

Wade Hampton Frost Popularized cohort analysis method. Arranged tuberculosis mortality rates in a table with age on one axis and year of death on the other. One can quickly see the age-specific mortality for each of the available years on one axis and the time trend for each age group on the other. Copyright 2004 Jones and Bartlett Publishers

Life Table Methods Give estimates for survival during time intervals and present the cumulative survival probability at the end of the interval. Example: Life tables can be constructed to portray the survival times of patients in clinical trials. Copyright 2004 Jones and Bartlett Publishers

Life Table Methods (cont’d)
There are two life table methods: Cohort Life Table Period (Current) Life Table Copyright 2004 Jones and Bartlett Publishers

Life Table Methods (cont’d)
Cohort life table: Shows the mortality experience of all persons born during a particular year. Period life table: Enables us to project the future life expectancy of persons born during the year as well as the remaining life expectancy of persons who have attained a certain age. Copyright 2004 Jones and Bartlett Publishers

Survival Curves A method for portraying survival times
To construct a survival curve, the following information is required: Time of entry into the study Time of death or other outcome Status of patient at time of outcome, e.g., dead or censored (patient is lost to follow-up) Copyright 2004 Jones and Bartlett Publishers

Survival Curves: Example
15 subjects followed over 36 months; all entered the study at the same time. Nine died at different points of the study. Deaths of two patients caused a steep drop at 19 months. Each step indicates the death(s) of one or more patients. Copyright 2004 Jones and Bartlett Publishers

Cohort Studies Start with a group of subjects who lack a positive history of the outcome of interest and are at risk for the outcome. Include at least two observation points: one to determine exposure status and eligibility and a second (or more) to determine the number of incident cases. Copyright 2004 Jones and Bartlett Publishers

Cohort Studies (cont’d)
Permit the calculation of incidence rates. Can be thought of as going from cause to effect. Involve the collection of primary data. Copyright 2004 Jones and Bartlett Publishers

Cohort Studies Timing of Data Collection

Sampling and Cohort Formation Options
Cohort studies differ according to sampling strategy used. The two strategies are population-based samples and exposure-based samples. Copyright 2004 Jones and Bartlett Publishers

Population-based Cohort Studies
The cohort includes either an entire population or a representative sample of the population. Population-based cohorts have been used in studies of coronary heart disease. Copyright 2004 Jones and Bartlett Publishers

Framingham Study Conducted in Framingham, Massachusetts. Ongoing study of CHD initiated in 1949. Used a random sample of 6,500 from targeted age range of 30 to 59 years. Copyright 2004 Jones and Bartlett Publishers

Tecumseh Study Conducted in Tecumseh, Michigan. A total community cohort study. Examined the contribution of environmental and constitutional factors to the maintenance of health and origins of illness. Started in and enrolled 8,641 (88% of the community). Copyright 2004 Jones and Bartlett Publishers

Population-based Cohort Studies (cont’d)
Exposures unknown until the first period of observation when exposure information is collected. There can be two or more levels of exposure. Copyright 2004 Jones and Bartlett Publishers

Exposure-based Cohort Studies
These studies overcome limitations of population-based cohort studies, which are not efficient for rare exposures. Certain groups, such as occupational groups, may have higher exposures than the general population to specific hazards. Copyright 2004 Jones and Bartlett Publishers

Definition of Exposure-based Cohort
An exposure-based cohort is made up of subjects with a common exposure, for example, workers exposed to lead during battery production. Copyright 2004 Jones and Bartlett Publishers

Comparison (Non-exposed Group)
Cohort studies involve the comparison of disease rates between exposed and non-exposed groups. The comparison group is similar in demographics and geography to the exposed group, but lacks the exposure. In an occupational setting, several categories of exposure may exist. Copyright 2004 Jones and Bartlett Publishers

Temporal Differences in Cohort Designs
There are several variations in cohort designs that depend on the timing of data collection. These variations are: prospective cohort studies retrospective cohort studies historical prospective cohort studies Copyright 2004 Jones and Bartlett Publishers

Prospective Cohort Study
Purely prospective in nature; characterized by determination of exposure levels at baseline (the present), and follow-up for occurrence of disease at some time in the future. Copyright 2004 Jones and Bartlett Publishers

Advantages of Prospective Cohort Studies
Enable the investigator to collect data on exposures; the most direct and specific test of the study hypothesis. The size of the cohort is under greater control by the investigators. Copyright 2004 Jones and Bartlett Publishers

Advantages of Prospective Cohort Studies (cont’d)
Biological and physiological assays can be performed with decreased concern that the outcome will be affected by the underlying disease process. Direct measures of the environment (e.g., indoor radon levels, electromagnetic field radiation, cigarette smoke concentration) can be made. Copyright 2004 Jones and Bartlett Publishers

Retrospective Cohort Study
Despite substantial benefits of prospective cohort studies, investigators have to wait for cases to accrue. Retrospective cohort studies make use of historical data to determine exposure level at some baseline in the past. Copyright 2004 Jones and Bartlett Publishers

Advantages of Retrospective Cohort Studies
A significant amount of follow-up may be accrued in a relatively short period of time. The amount of exposure data collected can be quite extensive and available to the investigator at minimal cost. Copyright 2004 Jones and Bartlett Publishers

Practical Considerations Regarding Cohort Studies
Availability of exposure data Size and cost of the cohort used Data collection and data management Follow-up issues Sufficiency of scientific justification Copyright 2004 Jones and Bartlett Publishers

Availability of Exposure Data
High quality historical exposure data are absolutely essential for retrospective cohort studies. Need to trade off between a retrospective study design (with the benefits of more immediate follow-up time) and collection of primary exposure data in a prospective cohort design. Copyright 2004 Jones and Bartlett Publishers

Size and Cost of the Cohort
The larger the size of the cohort, the greater the opportunity to obtain findings in a timely manner. Resource constraints typically influence design decisions. Copyright 2004 Jones and Bartlett Publishers

Data Collection and Data Management
Larger studies are more demanding than smaller ones; challenges due to data collection and data management. Explicit protocols for quality control (e.g., double entry of data and scannable forms) should be considered in the design and implementation stage. Copyright 2004 Jones and Bartlett Publishers

Data Collection and Data Management (cont’d)
Organizational and administrative burdens are increased when there are multiple levels of data collection (such as phone interviews, mailed questionnaires, consent forms to access medical records). Copyright 2004 Jones and Bartlett Publishers

Active Follow-up The investigator, through direct contact with the cohort, must obtain data on subsequent incidence of the outcome (disease, change in risk factor, change in biological marker). Accomplished through follow-up mailings, phone calls, or written invitations to return to study sites/centers. Copyright 2004 Jones and Bartlett Publishers

Active Follow-up (cont’d)
Example: Minnesota Breast Cancer Family Study Mailed survey A reminder postcard 30 days later A second survey A telephone call to non-responders Copyright 2004 Jones and Bartlett Publishers

Passive Follow-up Does not require direct contact with cohort members. Possible when databases containing the outcomes of interest are collected and maintained by organizations outside the investigative team. Example: Used in the Iowa Women’s Health Study. Copyright 2004 Jones and Bartlett Publishers

Sufficiency of Scientific Justification
There should be considerable scientific rationale for a cohort study. Additional justification for cohort studies may come from laboratory experiments or animal studies. Cohort studies are the only observational study design that permits examination of multiple outcomes. Copyright 2004 Jones and Bartlett Publishers

Cohort Studies: Measures of Association
Relative risk provides a direct measure of association between exposure and outcome. Relative risk is the ratio of the incidence of disease in the exposed group to the incidence in the non-exposed group. Copyright 2004 Jones and Bartlett Publishers

Measures of Association (cont’d)
Disease Status Incidence Exposure Yes No Totals Rate Status Yes A B A+B A/(A+B) No C D C+D C/(C+D) Relative Risk [A/A+B]/[C/C+D] Attributable Risk [A/A+B]-[C/C+D] Copyright 2004 Jones and Bartlett Publishers

Cohort Studies: Sample Calculation
Is there an association between child abuse and suicide attempts among chemically dependent adolescents? Source: Deykin EY, Buka SL. Am J Public Health. 1994;84: Copyright 2004 Jones and Bartlett Publishers

Sample Calculation (cont’d)
History of Sexual Abuse Suicide Attempt No Suicide Attempt Totals Yes A = 14 B = 9 A + B = 23 No C = 49 D = 149 C + D = 198 Relative Risk = (14/23) ÷ (49/198) = 2.46 Copyright 2004 Jones and Bartlett Publishers

Examples of Major Cohort Studies
The Alameda County Study Studied factors associated with health and mortality. Involved residents of Alameda County, CA, ages years. Data collected through mailed questionnaires; telephone interviews or home interviews of non-respondents. Follow-up with same procedures at years 9, 18, and 29. Copyright 2004 Jones and Bartlett Publishers

Examples of Major Cohort Studies (cont’d)
Honolulu Heart Program Studied coronary heart disease and stroke in men of Japanese ancestry. Involved men of Japanese ancestry living on Oahu, HI, ages years. Data collected through mailed questionnaires, interviews, and clinic examinations. Copyright 2004 Jones and Bartlett Publishers

Examples of Major Cohort Studies (cont’d)
Nurses’ Health Study Originally studied oral contraceptive use; expanded to women’s health. Married female R.N.s ages years. Data collected through mailed questionnaires. Follow-up every 2 years; toenail sample at year 6 and blood sample at year 13. Copyright 2004 Jones and Bartlett Publishers

Nested Case-Control Studies
Defined as a type of case-control study in which cases and controls are drawn from the population in a cohort study. The population of the cohort study comprises both exposed and non-exposed persons. Copyright 2004 Jones and Bartlett Publishers

Advantages of Nested Case-Control Studies
Provide a degree of control over confounding factors. Reduce cost because exposure information is collected from a subset of the cohort only. An example is an investigation of suicide among electric utility workers. Copyright 2004 Jones and Bartlett Publishers

Strengths of Cohort Studies
Permit direct determination of risk. Time sequencing of exposure and outcome. Can study multiple outcomes. Can study rare exposures. Copyright 2004 Jones and Bartlett Publishers

Limitations of Cohort Studies
Take a long time Costly Subjects lost to follow-up Copyright 2004 Jones and Bartlett Publishers

Experimental Study Designs
Chapter 8 Experimental Study Designs

Learning Objectives (abridged)
State how study designs compare with respect to validity of causal inference. Define the term controlled clinical trials. Define what is meant by community trials. Copyright 2004 Jones and Bartlett Publishers

Quasi-Experiment/Community Trial
Ranked immediately below controlled experiments in rigor. Investigator is unable to randomly allocate subjects to the conditions. There may be contamination across the conditions of the study. Copyright 2004 Jones and Bartlett Publishers

Intervention Studies Used to test efficacy of preventive or therapeutic measures. Two categories: Controlled clinical trials Community interventions Multicenter trials--results from several researchers are pooled. Copyright 2004 Jones and Bartlett Publishers

History of Clinical Trials
In 1537, Ambroise Paré applied experimental treatment for battlefield wounds. East India Shipping Company (1600) found that lemon juice protected against scurvy. James Lind (1747) used the concurrently treated control group method. Copyright 2004 Jones and Bartlett Publishers

Clinical Trials Definition
A planned experiment that assesses the efficacy of a treatment in man. Outcomes in treated group are compared with outcomes in an equivalent control group. Participants in both groups are enrolled, treated, and followed over the same time period. Copyright 2004 Jones and Bartlett Publishers

Clinical Trials Assess the efficacy of a treatment. Carefully designed and rigidly enforced protocol. Random assignment of subjects to study groups (intervention and control). Placebo given to control group. Copyright 2004 Jones and Bartlett Publishers

Clinical Trials (cont’d)
Eligibility rules carefully defined and rigidly enforced. Subjects are randomly assigned to one of the study groups, e.g., intervention or control (placebo). More than one experimental intervention can be run in parallel. Copyright 2004 Jones and Bartlett Publishers

Prophylactic and Therapeutic Trials
A prophylactic trial evaluates the effectiveness of a substance that is used to prevent disease; it can also involve a prevention program. A therapeutic trial involves the study of curative drugs or a new surgical procedure to improve the patient’s health. Copyright 2004 Jones and Bartlett Publishers

Outcomes of Clinical Trials
Referred to as clinical end points. May include rates of disease, death, or recovery. Outcomes must be measured in a comparable manner in the intervention and control conditions. Copyright 2004 Jones and Bartlett Publishers

Examples of Clinical Trials
Medical Research Council Vitamin Study—studied role of folic acid in preventing neural tube defects. South Bronx, NY, STD Program—evaluated effectiveness of education efforts to prevent spread of sexually transmitted diseases (STDs). Copyright 2004 Jones and Bartlett Publishers

Blinding (Masking) To maintain the integrity of a study and reduce the potential for bias, the investigator may utilize one of two popular approaches: Single-blind design: subject unaware of group assignment. Double-blind design: Neither subject nor experimenter is aware of group assignment. Copyright 2004 Jones and Bartlett Publishers

Phases of Clinical Trials
Before a vaccine, drug, or treatment can be licensed for general use, it must go through several stages of development. This lengthy process helps to protect the public, yet at the same time delays access to needed pharmaceutical agents for critically ill patients, such as those afflicted with AIDS or cancer. Copyright 2004 Jones and Bartlett Publishers

Phases of Clinical Trials for New Vaccines
Phase I--tests a new vaccine in adult volunteers (fewer than 100 volunteers). Phase II--expands testing to a group of 100 to 200 subjects (from the targeted population). Phase III (the main test)--assesses the efficacy of the vaccine in the target population. Copyright 2004 Jones and Bartlett Publishers

Randomization Method of choice for assigning subjects to the treatment or control conditions of a clinical trial. Non-random assignment may cause mixing of the effects of the intervention with differences (e.g., demographic) among the participants of the trial. Copyright 2004 Jones and Bartlett Publishers

Crossover Designs Any change of treatment for a patient in a clinical trial involving a switch of study treatments. In planned crossovers a protocol is developed in advance, and the patient may serve as his or her own control. Unplanned crossovers exist for various reasons, such as patient’s request to change treatment. Copyright 2004 Jones and Bartlett Publishers

Ethical Aspects of Human Experimentation
Benefits must outweigh risks. Ethical issues: Informed consent Withholding treatment Sequential designs are used as a solution. Monitoring for side effects Can be circumvented by using animals. Deciding when to withdraw a patient Protecting the interests of patients Copyright 2004 Jones and Bartlett Publishers

Reporting the Results of Clinical Trials
The CONSORT Statement is a protocol that guides the reporting of randomized trials by providing a 22-item checklist and a flowchart. Copyright 2004 Jones and Bartlett Publishers

Summary of Clinical Trials
Strengths: Provide the greatest control over: the amount of exposure the timing and frequency of exposure the period of observation Ability to randomize reduces the likelihood that groups will differ significantly. Copyright 2004 Jones and Bartlett Publishers

Summary of Clinical Trials (cont’d)
Limitations: Artificial setting Limited scope of potential impact Adherence to protocol is difficult to enforce. Ethical dilemmas Copyright 2004 Jones and Bartlett Publishers

Community Trials Community intervention trials determine the potential benefit of new policies and programs. Intervention: Any program or other planned effort designed to produce changes in a target population. Community refers to a defined unit, e.g., a county, state, or school district. Copyright 2004 Jones and Bartlett Publishers

Community Trials (cont’d)
Start by determining eligible communities and their willingness to participate. Collect baseline measures of the problem to be addressed in the intervention and control communities. Use a variety of measures, e.g., disease rates, knowledge, attitudes, and practices. Copyright 2004 Jones and Bartlett Publishers

Community Trials (cont’d)
Communities are randomized and followed over time. Outcomes of interest are measured. Copyright 2004 Jones and Bartlett Publishers

Examples of Community Trials
North Karelia Project Minnesota Heart Health Program Stanford Five-City Project Pawtucket Heart Health Program Community Intervention Trial for Smoking Cessation (COMMIT) Project Respect Copyright 2004 Jones and Bartlett Publishers

Summary of Community Trials: Advantages
Represent the only way to estimate directly the impact of change in behavior or modifiable exposure on the incidence of disease. Copyright 2004 Jones and Bartlett Publishers

Summary of Community Trials: Disadvantages
Inferior to clinical trials with respect to ability to control entrance into study, delivery of the intervention, and monitoring of outcomes. Fewer study units are capable of being randomized, which affects comparability. Affected by population dynamics, secular trends, and nonintervention influences. Copyright 2004 Jones and Bartlett Publishers

Evaluation of Community Interventions
Posttest only--observations are made only after the program has been delivered. Pretest/Posttest--baseline and follow-up observations are made. Pretest/Posttest/Control--observations are made in both intervention and control groups before and after the program. Copyright 2004 Jones and Bartlett Publishers

Evaluation of Community Interventions (cont’d)
Solomon Four-Group assignment: Used to overcome the Hawthorne Effect. Uses four equivalent groups, two intervention and two control: Two are observed before and after intervention. Two are observed only after intervention. Copyright 2004 Jones and Bartlett Publishers

Four Stages of Evaluation
Formative: Will all plans and procedures work as conceived? Process: Is the program serving the target group as planned? Impact: Has the program produced any changes among the target group? Outcome: Did the program accomplish its ultimate goal? Copyright 2004 Jones and Bartlett Publishers

Chapter 9 Measures of Effect

Risk Difference (Attributable Risk)
Risk difference--the difference between the incidence rate of disease in the exposed group (Ie) and the incidence rate of disease in the nonexposed group (Ine). Risk difference = Ie - Ine Copyright 2004 Jones and Bartlett Publishers 2

Calculation of Risk Difference
For women younger than age 75, the incidence (Ie) of hip fractures per 100,000 person-days was highest in the winter (0.41), and the incidence (Ine) was lowest in the summer (0.29). The risk difference between the two seasons (Ie - Ine) was , or 0.12 per 100,000 person-days. Copyright 2004 Jones and Bartlett Publishers 3

Statistical Measures of Effect
Significance tests The P value Confidence interval Copyright 2004 Jones and Bartlett Publishers 4

Significance Tests In order to decide whether or not to reject or fail to reject the null hypothesis, a test statistic is computed and compared with a critical value obtained from a set of statistical tables. Copyright 2004 Jones and Bartlett Publishers 6

The P Value Indicates the probability that the findings observed could have occurred by chance alone. However, a nonsignificant difference is not necessarily attributable to chance alone. Copyright 2004 Jones and Bartlett Publishers 8

The P Value (cont’d) Possible meaning of nonsignificant differences: -- For studies with a small sample size the sampling error may be large, which can lead to a nonsignificant test even if the observed difference is caused by a real effect. Copyright 2004 Jones and Bartlett Publishers

Confidence Interval (CI)
A computed interval of values that, with a given probability, contains the true value of the population parameter. The degree of confidence is usually stated as a percentage; commonly the 95% CI is used. Influenced by variability of the data and sample size. Copyright 2004 Jones and Bartlett Publishers 9

Clinical vs. Statistical Significance
While small differences in disease frequency or low magnitudes of relative risk (RR) may be significant, they may have no clinical significance. Conversely, with small sample sizes, large differences or measures of effect may be clinically important. Copyright 2004 Jones and Bartlett Publishers 10

Statistical Power The ability of a study to demonstrate an association if one exists. Determined by: Frequency of the condition under study. Magnitude of the effect. Study design. Sample size. Copyright 2004 Jones and Bartlett Publishers 11

Evaluating Epidemiologic Associations
Five key questions to be asked: Could the association have been observed by chance? Determined through the use of statistical tests. Could the association be due to bias? Bias refers to systematic errors, i.e., how samples were selected or how data was analyzed. Copyright 2004 Jones and Bartlett Publishers 12

Evaluating Epidemiologic Associations (cont’d)
Could other confounding variables have accounted for the observed relationship? To whom does this association apply? Representativeness of sample Participation rates Does the association represent a cause-and-effect relationship? Considers criteria of causality. Copyright 2004 Jones and Bartlett Publishers 13

Chapter 10 Data Interpretation Issues

Validity of Study Designs
Two components of validity: Internal validity External validity Copyright 2004 Jones and Bartlett Publishers 2

Internal Validity A study is said to have internal validity when there have been proper selection of study groups and a lack of error in measurement. Concerned with the appropriate measurement of exposure, outcome, and association between exposure and disease. Copyright 2004 Jones and Bartlett Publishers 3

Sources of Error in Epidemiologic Research
Random errors Systematic errors (bias) Copyright 2004 Jones and Bartlett Publishers 5

Factors That Contribute to Random Error
Poor precision Sampling error Variability in measurement Copyright 2004 Jones and Bartlett Publishers 7

Poor Precision Occurs when the factor being measured is not measured sharply. Analogous to aiming a rifle at a target that is not in focus. Precision can be increased by increasing sample size or the number of measurements. Copyright 2004 Jones and Bartlett Publishers 8

Sampling Error Occurs when the sample selected is not representative of the target population. Increasing the sample size can reduce the likelihood of sampling error. Copyright 2004 Jones and Bartlett Publishers 9

Variability in Measurement
The lack of agreement in results from time to time reflects random error inherent in the type of measurement procedure employed. Copyright 2004 Jones and Bartlett Publishers 10

Bias (Systematic Errors)
“Deviation of results or inferences from the truth, or processes leading to such deviation. Any trend in the collection, analysis, interpretation, publication, or review of data that can lead to conclusions that are systematically different from the truth.” Copyright 2004 Jones and Bartlett Publishers 11

Factors That Contribute to Systematic Errors
Selection bias Information bias Confounding Copyright 2004 Jones and Bartlett Publishers 12

Selection Bias Arises when the relation between exposure and disease is different for those who participate and those who theoretically would be eligible for study but do not participate. Example: Respondents to the Iowa Women’s Health Study were younger, weighed less, and were more likely to live in rural, less affluent counties than nonrespondents. Copyright 2004 Jones and Bartlett Publishers 13

Information Bias Can be introduced as a result of measurement error in assessment of both exposure and disease. Types of information bias: Recall bias: better recall among cases than among controls. Example: Family recall bias. Copyright 2004 Jones and Bartlett Publishers 14

Information Bias (cont’d)
Interviewer/abstractor bias--occurs when interviewers probe more thoroughly for an exposure in a case than in a control. Prevarication (lying) bias--occurs when participants have ulterior motives for answering a question and thus may underestimate or exaggerate an exposure. Copyright 2004 Jones and Bartlett Publishers 15

Confounding The distortion of the estimate of the effect of an exposure of interest because it is mixed with the effect of an extraneous factor. Occurs when the crude and adjusted measures of effect are not equal (difference of at least 10%). Can be controlled for in the data analysis. Copyright 2004 Jones and Bartlett Publishers 16

Criteria of Confounders
To be a confounder, an extraneous factor must satisfy the following criteria: Be a risk factor for the disease. Be associated with the exposure. Not be an intermediate step in the causal path between exposure and disease. Copyright 2004 Jones and Bartlett Publishers 17

Simpson’s Paradox as an Example of Confounding
Demonstrates that associations can be reversed when confounding factors are controlled. Illustrated by examining the data (% of black and gray hats) first according to two individual tables and then by combining all the hats on a single table. Copyright 2004 Jones and Bartlett Publishers

Examples of Confounding
Air pollution and bronchitis are positively associated. Both are influenced by crowding, a confounding variable. The association between high altitude and lower heart disease mortality also may be linked to the ethnic composition of the people in these regions. Copyright 2004 Jones and Bartlett Publishers 18

Techniques to Reduce Selection Bias
Develop an explicit (objective) case definition. Enroll all cases in a defined time and region. Strive for high participation rates. Take precautions to ensure representativeness. Copyright 2004 Jones and Bartlett Publishers 20

Reducing Selection Bias Among Cases
Ensure that all medical facilities are thoroughly canvassed. Develop an effective system for case ascertainment. Consider whether all cases require medical attention; consider possible strategies to identify where else the cases might be ascertained. Copyright 2004 Jones and Bartlett Publishers

Reducing Selection Bias Among Controls
Compare the prevalence of the exposure with other sources to evaluate credibility. Attempt to draw controls from a variety of sources. Copyright 2004 Jones and Bartlett Publishers 21

Techniques to Reduce Information Bias
Use memory aids; validate exposures. Blind interviewers as to subjects’ study status. Provide standardized training sessions and protocols. Use standardized data collection forms. Blind participants as to study goals and classification status. Copyright 2004 Jones and Bartlett Publishers 22

Methods to Control Confounding
Prevention strategies--attempt to control confounding through the study design itself. Three types of prevention strategies: Randomization Restriction Matching Copyright 2004 Jones and Bartlett Publishers 23

Randomization Attempts to ensure equal distributions of the confounding variable in each exposure category. Advantages: Convenient, inexpensive; permits straightforward data analysis. Disadvantages: Need control over the exposure and the ability to assign subjects to study groups. Need large sample sizes. Copyright 2004 Jones and Bartlett Publishers 24

Restriction May prohibit variation of the confounder in the study groups. For example, restricting participants to a narrow age category can eliminate age as a confounder. Provides complete control of known confounders. Unlike randomization, cannot control for unknown confounders. Copyright 2004 Jones and Bartlett Publishers 25

Matching Matches subjects in the study groups according to the value of the suspected or known confounding variable to ensure equal distributions. Frequency matching--the number of cases with particular match characteristics is tabulated. Individual matching--the pairing of one or more controls to each case based on similarity in sex, race, or other variables. Copyright 2004 Jones and Bartlett Publishers 26

Matching (cont’d) Advantages: Fewer subjects are required than in unmatched studies of the same hypothesis. May enhance the validity of a follow-up study. Disadvantages: Costly because extensive searching and recordkeeping are required to find matches. Copyright 2004 Jones and Bartlett Publishers 27

Two Analysis Strategies to Control Confounding
Stratification--analyses performed to evaluate the effect of an exposure within strata (levels) of the confounder. Multivariate techniques--use computers to construct mathematical models that describe simultaneously the influence of exposure and other factors that may be confounding the effect. Copyright 2004 Jones and Bartlett Publishers 28

Advantages of Stratification
Performing analyses within strata is a direct and logical strategy. Minimum assumptions must be satisfied for the analysis to be appropriate. The computational procedure is straightforward. Copyright 2004 Jones and Bartlett Publishers 29

Disadvantages of Stratification
Small numbers of observations in some strata. A variety of ways to form strata with continuous variables. Difficulty in interpretation when several confounding factors must be evaluated. Categorization produces loss of information. Copyright 2004 Jones and Bartlett Publishers 30

Multivariate Techniques
Advantages: Continuous variables do not need to be converted to categorical variables. Allow for simultaneous control of several exposure variables in a single analysis. Disadvantages: Potential for misuse. Copyright 2004 Jones and Bartlett Publishers 31

Publication Bias Occurs because of the influence of study results on the chance of publication. Studies with positive results are more likely to be published than studies with negative results. Copyright 2004 Jones and Bartlett Publishers

Publication Bias (cont’d)
May result in a preponderance of false-positive results in the literature. Bias is compounded when published studies are subjected to meta-analysis. Copyright 2004 Jones and Bartlett Publishers

Chapter 11 Screening for Disease in the Community

Screening for Disease Screening--the presumptive identification of unrecognized disease or defects by the application of tests, examinations, or other procedures that can be applied rapidly. Positive screening results are followed by diagnostic tests to confirm actual disease. Copyright 2004 Jones and Bartlett Publishers

Multiphasic Screening
Defined as the use of two or more screening tests together among large groups of people. Information obtained on risk factor status, history of illness, and health measurements. Commonly used by employers and health maintenance organizations. Copyright 2004 Jones and Bartlett Publishers

Mass Screening and Selective Screening
Mass screening--screening on a large scale of total population groups regardless of risk status. Selective screening--screens subsets of the population at high risk for disease. More economical, and likely to yield more true cases. Example: Screening high-risk persons for Tay-Sachs disease. Copyright 2004 Jones and Bartlett Publishers

Mass Health Examinations
Population or epidemiologic surveys--purpose is to gain knowledge regarding the distribution and determinants of diseases in selected populations. No benefit to the participant is implied. Copyright 2004 Jones and Bartlett Publishers

Mass Health Examinations (cont’d)
Epidemiologic surveillance--aims at the protection of community health through case detection and intervention. Case finding (opportunistic screening)--the utilization of screening tests for detection of conditions unrelated to the patient’s chief complaint. Copyright 2004 Jones and Bartlett Publishers

Appropriate Situations for Screening Tests and Programs
Social Scientific Ethical Copyright 2004 Jones and Bartlett Publishers

Social The health problem should be important for the individual and the community. Diagnostic follow-up and intervention should be available to all who require them. There should be a favorable cost-benefit ratio. Public acceptance must be high. Copyright 2004 Jones and Bartlett Publishers

Scientific Natural history of the condition should be adequately understood. This knowledge permits identification of early stages of disease and appropriate biologic markers of progression. Prevalence of the disease or condition is high. Copyright 2004 Jones and Bartlett Publishers

Ethical The program can alter the natural history of the condition in a significant proportion of those screened. Suitable, acceptable tests for screening and diagnosis of the condition as well as acceptable, effective methods of prevention are available. Copyright 2004 Jones and Bartlett Publishers

Characteristics of a Good Screening Test
Simple--easy to learn and perform. Rapid--quick to administer; results available rapidly. Inexpensive--good cost-benefit ratio. Safe--no harm to participants. Acceptable--to target group. Copyright 2004 Jones and Bartlett Publishers

Evaluation of Screening Tests
Reliability types Repeated measurements Internal consistency Interjudge Validity types Content Criterion-referenced Predictive Concurrent Construct Copyright 2004 Jones and Bartlett Publishers

Reliability (Precision)
The ability of a measuring instrument to give consistent results on repeated trials. Repeated measurement reliability--the degree of consistency among repeated measurements of the same individual on more than one occasion. Copyright 2004 Jones and Bartlett Publishers

Reliability (cont’d) Internal consistency reliability--evaluates the degree of agreement or homogeneity within a questionnaire measure of an attitude, personal characteristic, or psychologic attribute. Interjudge reliability--reliability assessments derived from agreement among trained experts. Copyright 2004 Jones and Bartlett Publishers

Validity (Accuracy) The ability of a measuring instrument to give a true measure. Can be evaluated only if an accepted and independent method for confirming the test measurement exists. Copyright 2004 Jones and Bartlett Publishers

Validity (cont’d) Content validity--the degree to which a measure covers the range of meanings included within the concept. Criterion-referenced validity--found by correlating a measure with an external criterion of the entity being assessed. Copyright 2004 Jones and Bartlett Publishers

Validity (cont’d) Two types of criterion-referenced validity: Predictive validity--denotes the ability of a measure to predict some attribute or characteristic in the future. Concurrent validity--obtained by correlating a measure with an alternative measure of the same phenomenon taken at the same point in time. Copyright 2004 Jones and Bartlett Publishers

Interrelationships Between Reliability and Validity
It is possible for a measure to be highly reliable but invalid. It is not possible for a measure to be valid but unreliable. Copyright 2004 Jones and Bartlett Publishers

Representation of Reliability and Validity

Sources of Unreliability and Invalidity
Measurement bias--constant errors that are introduced by a faulty measuring device and tend to reduce the reliability of measurements. Example: A miscalibrated blood pressure manometer. Copyright 2004 Jones and Bartlett Publishers

Sources of Unreliability and Invalidity (cont’d)
Halo effect--bias that affects the validity of questionnaire measurements. Example: All items of a checklist evaluation of an employee may be filled out in the same general direction based on the supervisor’s opinion of the individual. Social desirability effects Respondent answers questions in a manner that agrees with desirable social norms. Copyright 2004 Jones and Bartlett Publishers

Measures of the Validity of Screening Tests
Sensitivity--the ability of the test to identify correctly all screened individuals who actually have the disease (a/a+c). Specificity--the ability of the test to identify only nondiseased individuals who actually do not have the disease (d/b+d). Copyright 2004 Jones and Bartlett Publishers

Measures of the Validity of Screening Tests (cont’d)
Predictive value (+)--the proportion of individuals screened positive by the test who actually have the disease (a/a+b). Predictive value (-)--the proportion of individuals screened negative by the test who do not have the disease (d/c+d). Copyright 2004 Jones and Bartlett Publishers

Other Measures from the 2 by 2 Table
Accuracy of a screening test--determined by the formula: (a+d)/(a+b+c+d). Prevalence--determined by the formula: (a+c)/(a+b+c+d) Copyright 2004 Jones and Bartlett Publishers

Effects of Disease Prevalence on the Predictive Value of a Screening Test When the prevalence of a disease falls, the predictive value (+) falls, and the predictive value (-) rises. Copyright 2004 Jones and Bartlett Publishers

Relationship Between Sensitivity and Specificity
To improve sensitivity, the cut point used to classify individuals as diseased should be moved farther in the range of the nondiseased (normals). To improve specificity, the cut point should be moved farther in the range typically associated with the disease. Copyright 2004 Jones and Bartlett Publishers

Relationship (cont’d)

Procedures to Improve Sensitivity and Specificity
Retrain screeners--reduces the amount of misclassification in tests that require human assessment. Recalibrate screening instrument--reduces the amount of imprecision. Utilize a different test. Utilize more than one test. Copyright 2004 Jones and Bartlett Publishers

Evaluation of Screening Programs
Randomized control trials Subjects receive either the new screening test or usual care. Ecologic time trend studies Compare geographic regions with screening programs to those without. Case-control studies Cases--fatal cases of the disease. Controls--nonfatal cases. Exposure--screening program. Copyright 2004 Jones and Bartlett Publishers

Sources of Screening Evaluation Bias
Lead time bias The perception that the screen-detected case has longer survival because the disease was identified early. Length bias Particularly relevant to cancer screening. Tumors identified by screening are slower growing and have a better prognosis. Selection bias Motivated participants have a different probability of disease than do those who refuse to participate. Copyright 2004 Jones and Bartlett Publishers

Natural History of Disease

Issues in the Classification of Morbidity and Mortality
The nomenclature and classification of disease are central to the reliable measurement of the outcome variable in epidemiologic research. Nomenclature--a highly specific set of terms for describing and recording clinical or pathologic diagnoses to classify ill persons into groups. Copyright 2004 Jones and Bartlett Publishers

Issues in the Classification of Morbidity and Mortality (cont’d)
Classification--the statistical compilation of groups of cases of disease by arranging disease entities into categories that share similar features. Two types of criteria used for the classification of ill persons: Causal Manifestational Copyright 2004 Jones and Bartlett Publishers

Chapter 12 Epidemiology of Infectious Diseases

Epidemiologic Triangle
A model used to explain the etiology of infectious diseases. Recognizes three major factors in the pathogenesis of disease: agent, host, and environment. Copyright 2004 Jones and Bartlett Publishers 2

Diagram of Epidemiologic Triangle

Microbial Agents of Infectious Disease
Bacteria Viruses and rickettsia Mycoses (fungal diseases) Protozoa Helminths Arthropods Copyright 2004 Jones and Bartlett Publishers 3

Bacteria Once were the leading killers, but now are controlled by antibiotics. Remain significant causes of human illness. Tuberculosis and salmonellosis are common diseases caused by bacteria. Copyright 2004 Jones and Bartlett Publishers

Viruses and Rickettsia
Viral hepatitis A, herpes, and influenza are caused by viruses. Rickettsial agents produce Q fever and Rocky Mountain spotted fever. Copyright 2004 Jones and Bartlett Publishers

Mycoses (Fungal Diseases)
Valley fever (coccidioidomycosis), ringworm and athlete’s foot. Opportunistic mycoses infect immunocompromised patients. Candidiasis, cryptococcosis, and aspergillosis. Copyright 2004 Jones and Bartlett Publishers 4

Helminths Found in tropical areas. Include intestinal parasites such as roundworms, pinworms, and tapeworms. Are responsible for trichinellosis and schistosomiasis. Copyright 2004 Jones and Bartlett Publishers

Characteristics of Infectious Disease Agents
Infectivity The capacity of an agent to produce infection or disease. Measured by the secondary attack rate. Pathogenicity The capacity of the agent to cause disease in the infected host. Measured by the proportion of individuals with clinically apparent disease. Copyright 2004 Jones and Bartlett Publishers 6

Characteristics of Infectious Disease Agents (cont’d)
Virulence Refers to the severity of the disease. Measured by the proportion of severe or fatal cases. If fatal, use case fatality rate. Toxigenicity The capacity of the agent to produce a toxin or poison. Copyright 2004 Jones and Bartlett Publishers 7

Characteristics of Infectious Disease Agents (cont’d)
Resistance The ability of the agent to survive adverse environmental conditions. Antigenicity The ability of the agent to induce antibody production in the host. Related to immunogenicity. Copyright 2004 Jones and Bartlett Publishers 8

Host: Definition (Refer to Glossary)
A person (or animal) who permits lodgment of an infectious disease agent under natural conditions. Copyright 2004 Jones and Bartlett Publishers

Host Once an agent infects the host, the degree and severity of the infection will depend on the host’s ability to fight off the infectious agent. Two types of defense mechanisms are present in the host: nonspecific and disease-specific. Copyright 2004 Jones and Bartlett Publishers 9

Nonspecific Defense Mechanisms
Examples include skin, mucosal surfaces, tears, saliva, gastric juices, and the immune system. Nonspecific defense mechanisms such as immunity may decrease as we age. Copyright 2004 Jones and Bartlett Publishers 10

Disease-Specific Defense Mechanisms
Immunity (resistance) against a particular agent. Types of immunity: Active: administration of a microorganism to invoke an immunologic response that mimics the natural infection. Passive: short-term immunity provided by a preformed antibody. Copyright 2004 Jones and Bartlett Publishers 11

Active Immunity Natural, active--results from an infection by the agent. Artificial, active--results from an injection with a vaccine that stimulates antibody production in the host. Copyright 2004 Jones and Bartlett Publishers 12

Passive Immunity Natural, passive--preformed antibodies are passed to the fetus during pregnancy and provide short-term immunity in the newborn. Artificial, passive--preformed antibodies are given to exposed individuals to prevent disease. Copyright 2004 Jones and Bartlett Publishers

Environment The domain external to the host in which the agent may exist, survive, or originate. The environment consists of physical, climatologic, biologic, social, and economic components that affect the survival of the agents and serve to bring the agent and host into contact. Copyright 2004 Jones and Bartlett Publishers 13

Reservoirs of Infectious Diseases
The environment can act as a reservoir that fosters the survival of infectious agents. Examples: contaminated water supplies or food; soils; vertebrate animals. Copyright 2004 Jones and Bartlett Publishers 14

Animal Reservoirs Animals can be reservoirs of infectious agents. Zoonoses--infectious diseases that are potentially transmittable to humans by vertebrate animals. Examples: rabies and the plague. Copyright 2004 Jones and Bartlett Publishers

Direct Transmission from Reservoir
Spread of infection through person-to-person contact. Portal of exit--site where infectious agents leave the body, e.g., respiratory system, skin lesions. Copyright 2004 Jones and Bartlett Publishers 15

Direct Transmission (cont’d)
Portal of entry--locus of access to the human body, e.g., mouth and digestive system. Agent must exit in large enough quantities to survive in the environment and overcome the defenses at the portal of entry into the host. Copyright 2004 Jones and Bartlett Publishers

Inapparent Infection No symptoms of infection present. Important because disease can be transmitted to unsuspecting hosts. In asymptomatic individuals, clinicians can look for serologic evidence of infection. Example: Increase in antibodies and enzymes in patients with hepatitis A virus. Copyright 2004 Jones and Bartlett Publishers 16

Incubation Period The time interval between exposure to an infectious agent and the appearance of the first signs and symptoms of disease. Provides a clue to the time and circumstance of exposure to the agent. Useful for determining the etiologic agent. Copyright 2004 Jones and Bartlett Publishers 17

Herd Immunity Immunity of a population, group, or community against an infectious disease when a large proportion of individuals are immune either through vaccinations or prior infection. Copyright 2004 Jones and Bartlett Publishers 18

Generation Time Time interval between lodgment of an infectious agent in a host and the maximal communicability of the host. Can precede the development of active symptoms. Useful for describing the spread of infectious agents that have large proportions of subclinical cases. Copyright 2004 Jones and Bartlett Publishers 19

Colonization and Infestation
Colonization--agents multiply on the surface of the body without invoking tissue or immune response. Infestation--the presence of a living infectious agent on the body’s exterior surface, upon which a local reaction may be invoked. Copyright 2004 Jones and Bartlett Publishers 20

Iceberg Concept of Infection
Active clinical disease accounts for only a small proportion of host’s infections and exposures to disease agents. (Refer to next slide.) Copyright 2004 Jones and Bartlett Publishers 21

Iceberg Concept (cont’d)

Indirect Transmission
The spread of infection through an intermediary source: Vehicles--e.g., contaminated water, infected blood, food. Fomites--inanimate objects laden with disease-causing agents. Vectors--living insects or animals involved with transmission of the disease agent. Copyright 2004 Jones and Bartlett Publishers 22

Measures of Disease Outbreaks
Attack rate Secondary attack rate Case fatality rate Copyright 2004 Jones and Bartlett Publishers 23

Attack Rate Incidence rate that is used when the nature of the disease or condition is such that a population is observed for a short period of time. Formula: ___Ill __ X 100 during a time period Ill + Well Copyright 2004 Jones and Bartlett Publishers 24

Secondary Attack Rate An index of the spread of disease in a family, household, dwelling unit, dormitory or similar circumscribed group. A measure of contagiousness. Useful in evaluating control measures. Copyright 2004 Jones and Bartlett Publishers 25

Secondary Attack Rate: Definition
The number of cases of infection that occur among contacts within the incubation period following exposure to a primary case in relation to the total number of exposed contacts. Copyright 2004 Jones and Bartlett Publishers

Secondary Attack Rate (%) (Multiply fraction by 100.)
Number of new cases in group - initial case(s) Number of susceptible persons in the group - initial case(s) Initial case(s) = Index case(s) + coprimaries Index case(s) = Case that first comes to the attention of public health authorities. Coprimaries = Cases related to index case so closely in time that they are considered to belong to the same generation of cases. Copyright 2004 Jones and Bartlett Publishers 26

Case Fatality Rate (CFR)
The number of deaths caused by a disease among those who have the disease. Examples of diseases with a high CFR are rabies and AIDS. Copyright 2004 Jones and Bartlett Publishers 27

Formula For CFR Number of deaths due to disease “X “ x Number of cases of disease “X “ Sample calculation: Assume that an outbreak of plague occurs in an Asian country. Health authorities record 98 case of the disease, all of whom are untreated. Among these, 60 deaths are reported. CFR = (60/98) x 100 = 61.2% Copyright 2004 Jones and Bartlett Publishers 28

Investigation of Infectious Disease Outbreaks
Define the problem. Appraise existing data. Case identification Clinical observations Tabulation and spot maps Identification of responsible agent Copyright 2004 Jones and Bartlett Publishers 29

Investigation (cont’d)
Formulate a hypothesis. Test the hypothesis. Draw conclusions and formulate practical applications. Copyright 2004 Jones and Bartlett Publishers

Epidemiologically Significant Infectious Diseases
Food-borne illness Water- and food-borne diseases Sexually transmitted diseases Vaccine-preventable diseases Diseases spread by person-to-person contact Zoonotic diseases Arthropod-borne diseases Fungal diseases Copyright 2004 Jones and Bartlett Publishers 30

Food-borne Illness One of the most common infectious disease problems in the community. Examples include: Staphylococcus aureus--present in contaminated food. Produces a toxin. Trichinosis--associated with inadequately cooked pork products. Copyright 2004 Jones and Bartlett Publishers 31

Water- and Food-borne Diseases
Examples include: Amebiasis--intestinal disease. Cholera--acute enteric disease. Giardiasis Legionellosis Schistosomiasis--infection caused by adult worms in the bloodstream. The cycle involves alternate snail and human hosts. Copyright 2004 Jones and Bartlett Publishers 32

Sexually Transmitted Diseases: AIDS, 1981-2000
Characteristics of persons with AIDS: Greater increase in cases among females than males; still more males than females. Greatest impact among men who have sex with men and among racial/ethnic minorities. Number of persons living with AIDS has increased as deaths have declined. Copyright 2004 Jones and Bartlett Publishers 33

Vaccine-Preventable Diseases
Vaccines are routinely given to children for the prevention of the following nine diseases: Diphtheria, Haemophilus influenzae type b infections, hepatitis B, measles, mumps, pertussis, paralytic poliomyelitis, rubella, and tetanus. Copyright 2004 Jones and Bartlett Publishers 34

Diseases Spread by Person-to-Person Contact
One example is tuberculosis. Resurgence of TB due to: Increase in persons infected with HIV. Increase in homeless population. Importation of cases from endemic areas. Copyright 2004 Jones and Bartlett Publishers 35

U.S. TB Cases, Source: Reprinted from Centers for Disease Control and Prevention. Tuberculosis morbidity—United States, 1992. MMWR, vol 42, p 696, September 17, 1993. Copyright 2004 Jones and Bartlett Publishers

Zoonotic Diseases Zoonosis--a disease that under natural conditions can be spread from vertebrate animals to humans. Example: Q fever. Zoonotic diseases may be either: Enzootic--similar to endemic in human diseases. Epizootic--similar to epidemic in human diseases. Copyright 2004 Jones and Bartlett Publishers 36

Mycoses Coccidioidomycosis (San Joaquin Valley fever )--caused by the fungus Coccidioides immitis. Usually attacks the lungs. Cases of infection usually have had contact with contaminated soil. Other examples: blastomycosis, ringworm, athlete’s foot, candidiasis, cryptococcosis, and aspergillosis. Copyright 2004 Jones and Bartlett Publishers

Arthropod-borne Diseases
Include arboviral diseases. Blood-feeding arthropod vectors transmit disease agents to vertebrate hosts. Examples of vectors: sand flies, ticks, mosquitoes. Examples of diseases: encephalitis, Lyme disease Copyright 2004 Jones and Bartlett Publishers

Emerging Infections Suddenly increase in incidence or geographic scope. Many infections appear when an existing pathogen gains access to new host populations. Examples: U.S. hantaviral pulmonary syndrome, Lyme disease, AIDS, hepatitis C, hemorrhagic fever. Environmental changes may contribute to their emergence. Copyright 2004 Jones and Bartlett Publishers

Chapter 13 Epidemiologic Aspects of Work and the Environment

Human Exposures to Environmental Hazards
Chemical agents Electromagnetic radiation Ionizing radiation Heavy metals Air pollution Copyright 2004 Jones and Bartlett Publishers

Health Effects Attributed to Environmental Exposures
Cancer Congenital malformations Low birth weight Copyright 2004 Jones and Bartlett Publishers

Hazardous Agents in the Work Environment
Ionizing radiation Infectious agents Toxic substances Drugs Carcinogenic agents Copyright 2004 Jones and Bartlett Publishers

Health Effects Associated with Work Environment
Health risks for pregnant workers and the unborn fetus Various lung diseases Dermatologic problems Bladder cancer among dye workers Leukemia among workers exposed to benzene Copyright 2004 Jones and Bartlett Publishers 2

Study Designs Used in Environmental Epidemiology
Descriptive studies provide information for setting priorities, identifying hazards, and formulating hypotheses for new occupational risks. Etiologic studies can be used to show exposure-effect relationships. Copyright 2004 Jones and Bartlett Publishers 3

Retrospective Cohort Studies
Various end points are used to study the effects of occupational exposures. Morbidity: self-reports of symptoms and results of clinical examinations. Mortality: comparison of mortality rates of exposed workers with nonexposed workers in the same industry. Copyright 2004 Jones and Bartlett Publishers 4

Collection of Exposure Data
Employment records often are used and may include: Personal identifiers to permit record linkage. Demographic characteristics. Work history. Information about potential confounding variables, e.g., medical history, smoking habits. Copyright 2004 Jones and Bartlett Publishers 5

The Healthy Worker Effect
Observation that employed populations tend to have a lower mortality experience than the general population. The healthy worker effect may reduce the measure of effect for an exposure that increases morbidity or mortality. Copyright 2004 Jones and Bartlett Publishers 6

Ecologic Study Designs
One use is the study of the health effects of air pollution. Researchers measure the association between average exposure to air pollution within census tracts and the average mortality in those census tracts. Unable to controI for individual factors, e.g., smoking habits. Copyright 2004 Jones and Bartlett Publishers 7

Case-Control Studies Compared with cross-sectional study designs, case-control studies can provide more complete exposure data. However, precise quantitation of exposure and unobserved confounding may be difficult to achieve. Copyright 2004 Jones and Bartlett Publishers 8

Toxicologic Concepts Related to Environmental Epidemiology
Dose-response Threshold Latency Synergism Copyright 2004 Jones and Bartlett Publishers 9

Latency The time period between initial exposure and a measurable response. Latency can range from seconds (acute toxic agents) to years (mesothelioma). The long latency of health events in environmental research makes the detection of hazards difficult. Copyright 2004 Jones and Bartlett Publishers 12

Synergism Refers to a situation in which the combined effect of several exposures is greater than the sum of the individual effects. Example: Study conducted among asbestos insulation workers clearly demonstrated a synergistic relationship between asbestos and smoking in causing lung cancer. Copyright 2004 Jones and Bartlett Publishers 13

Chemical Agents Potential effects on human health through acute toxicity, direct skin irritation, contact dermatitis, or long-term effects such as cancer. Exposure to chemicals in occupational settings averages 1 to 100 times that in the ambient environment. Examples include pesticides and vinyl chloride. Copyright 2004 Jones and Bartlett Publishers 15

Chemical Agents (cont’d)
Pesticides--Examples are DDT, polychlorobiphenyls, and atrazine; linked to cancer, teratogenic effects, and cognitive deficits. Vinyl chloride--used in the plastics industry; associated with angiosarcoma of the liver, cancers of the lung, and central nervous system tumors. Copyright 2004 Jones and Bartlett Publishers 16

Chemical Agents (cont’d)
Asbestos Strictly speaking, a mineral fiber. Was used commonly for ship building, construction, insulation, and automobiles. Associated with asbestosis, mesothelioma, and lung cancer. Copyright 2004 Jones and Bartlett Publishers

Metallic Compounds Mercury Used for the treatment of syphilis, as an agricultural fungicide, and in dental amalgams. Responsible for Minamata disease, which occurred in the mid-1950s in Minamata Bay, Japan. A neurological condition linked to the consumption of fish contaminated with mercury. Copyright 2004 Jones and Bartlett Publishers 17

Metallic Compounds (cont’d)
Lead Once widely used in paint and gasoline. Associated with serious central nervous system effects even at low levels. Lead poisoning is one of the most common environmental pediatric health problems in the U.S. Has adverse effects on intelligence, behavior, and development. Copyright 2004 Jones and Bartlett Publishers 18

Electric and Magnetic Fields
Sources include power lines, microwave ovens, stoves, clocks, cellular phones. Los Angeles and Swedish studies found an association between residential proximity to power lines and childhood cancer risk. U.S. and Norwegian studies found an increased risk for male breast cancer among male electrical workers. Copyright 2004 Jones and Bartlett Publishers 19

Ionizing Radiation (cont’d)
Natural sources--examples are radon and cosmic rays. Environmental radon is the greatest source of human exposure to ionizing radiation and may be the cause of nearly 20% of U.S. lung cancers. Synthetic sources--examples are medical x-rays and nuclear generators. Copyright 2004 Jones and Bartlett Publishers

Allergens and Molds Allergens--substances that provoke an allergic reaction in susceptible individuals. Allergic reactions range from dermatitis, asthma, and itchy eyes to anaphylactic shock. Copyright 2004 Jones and Bartlett Publishers 21

Physical and Mechanical Energy
Include agents associated with accidental injury. Also include such factors as noise, vibration, and extremes of temperature. Copyright 2004 Jones and Bartlett Publishers 22

Monitoring and Surveillance of Occupational Hazards
Hazard surveillance--characterization of known chemical, physical, and biologic agents in the workplace. Sentinel health event--a case of unnecessary disease, unnecessary disability, or untimely death whose occurrence is a warning signal that the quality of preventive or medical care may need to be improved. Copyright 2004 Jones and Bartlett Publishers 23

Environmental Hazards Found in the Work Setting
Biologic hazards--Hospital employees, sewage workers, and agricultural workers may be exposed to hazardous biologic agents. For example, HIV may infect hospital workers through accidental needle sticks. Mineral and organic dusts--Examples include coal dust (mining and black lung disease) and rubber dust (COPD). Copyright 2004 Jones and Bartlett Publishers 24

Environmental Hazards Found in the Work Setting (cont’d)
Vapors--Include organic solvents such as benzene, which may cause cancer and damage internal organs (particularly the liver). Fumes and vapors are likely to become increasing hazards due to the growing use of chemical substances. Copyright 2004 Jones and Bartlett Publishers 25

Psychosocial Aspects of Employment and Health
Research topics include work overload and coronary heart disease; job stresses and absenteeism; and health effects of physical activity at work. For example, one study found an association between work stress and periodontal disease. Copyright 2004 Jones and Bartlett Publishers 26

Noteworthy Community Environmental Health Hazards
Hazardous waste sites Air pollution Nuclear facilities Drinking water Copyright 2004 Jones and Bartlett Publishers 27

Hazardous Waste Sites Notorious sites in the U.S. include: Love Canal, NY; Valley of the Drums, KY; Times Beach, MO; Stringfellow acid pits, CA. Of great concern is the contamination of water supplies by toxic wastes. Some possible adverse effects of hazardous waste exposure include birth defects, neurologic disease, and cancer. Copyright 2004 Jones and Bartlett Publishers 28

Air Pollution Constituents of air pollution include sulfur oxides, particulates, ozone, and lead and other heavy metals. Lethal air pollution episodes have occurred worldwide. Studies conducted in New York City, St. Louis, and Tennessee have shown a correlation between increases in daily mortality and increased air pollution. Copyright 2004 Jones and Bartlett Publishers 29

Environmental Tobacco Smoke (ETS)
Nonsmokers who work in a smoking environment have reduced pulmonary function compared to nonsmokers in a smoke-free work environment. ETS causes 3,000 lung cancer deaths annually among non-smokers. ETS is associated with children’s bronchitis, pneumonia, and asthma. Copyright 2004 Jones and Bartlett Publishers 30

Nuclear Facilities Include weapons production plants, test sites, and nuclear power plants. Studies of living in close proximity to nuclear installations have shown conflicting results regarding cancer rates. Following the Chernobyl nuclear power plant accident, thyroid cancer rates have increased near the reactor. Copyright 2004 Jones and Bartlett Publishers 31

Drinking Water Chemical plants and nuclear facilities may contaminate ground water. Chlorination of water supply has helped to decrease the incidence of gastroenteric diseases. Lead and asbestos particles may be present in water and have potential for toxicity. Copyright 2004 Jones and Bartlett Publishers 32

Chapter 14 Molecular and Genetic Epidemiology

Peeking into the “Black Box”
Many risk factors can be quantified through questionnaires, records, and easily measured attributes (such as blood pressure and anthropometrics). The biological mechanism(s) through which these factors influence disease is not always apparent (i.e., a “black box”). Copyright 2004 Jones and Bartlett Publishers

Value of Mechanistic Insight
Biologic plausibility is a criterion for causality. Linking lifestyle risk factors with measures of biologic effect strengthens interpretations of causality. This linkage, in turn, provides stronger support for interventions. Copyright 2004 Jones and Bartlett Publishers

Why Distinguish Between Molecular and Genetic Epidemiology?
The basic tenets and principles of molecular and genetic epidemiology are the same. However, there are specific features regarding design, analysis and interpretation inherent in the latter. Copyright 2004 Jones and Bartlett Publishers 3

Definition of Genetic Epidemiology
A discipline that seeks to unravel the role of genetic factors -- and their interactions with environmental factors – in the etiology of diseases, using family and population study approaches. Copyright 2004 Jones and Bartlett Publishers 4

Key Aspects of This Definition
Inherited susceptibility does not mean inherited disease--environment matters! When families are studied, the observations (study subjects) are no longer independent. This dependence requires special considerations for the analysis of data. Copyright 2004 Jones and Bartlett Publishers 5

Genetic Epidemiology is a Method to Answer the Questions:
Does a disease cluster in families? If so, is that clustering likely a result of shared non-genetic risk factors? If the clustering is not accounted for by shared lifestyle or common environment, is the pattern of disease consistent with inherited effects? If so, where is the putative gene? Copyright 2004 Jones and Bartlett Publishers 6

What Diseases or Risk Factors Cluster in Families?
Heart disease Various cancers Alcoholism Others Copyright 2004 Jones and Bartlett Publishers

Epidemiologic Assessment of Clustering
Case-control study Comparison of the frequency of a positive family history Expectation under genetic influence Copyright 2004 Jones and Bartlett Publishers

Clustering of “Non-Genetic” Exposures in Families
Employment (e.g., several family members with medical degrees) Radon from soil Religious preferences Lead in paint Others? Copyright 2004 Jones and Bartlett Publishers 7

Major Point of This Section
You cannot tell easily whether clustering of a risk factor or disease within a family is due to genetics, culture, or shared environment (including social or political factors). Copyright 2004 Jones and Bartlett Publishers 8

Other Correlates of Family History
Large family size Age of relatives (for an age-related disease) Gender distribution (consider testicular cancer, prostate disease, ovarian cysts) Copyright 2004 Jones and Bartlett Publishers

Analysis Approach Model Y (case/control status) = established risk factors. Add family history variable to denote “genetic” influence (i.e., share genes with an individual who has the outcome of interest). Copyright 2004 Jones and Bartlett Publishers

Analysis Issues Try to compare (and control if necessary) differences between cases and controls with regard to size of family. Not easy to adjust for age of family members or their risk factors. What types of data can you ask your cases and controls to provide about their relatives? Copyright 2004 Jones and Bartlett Publishers

Motivation for Case-Control Family Studies
To rule out influence of shared environment, family size differences, and age on differences in the frequency of family history between cases and controls. Need to enumerate the relatives of cases and controls, and determine the disease status and risk factor profile for each relative. Copyright 2004 Jones and Bartlett Publishers

Conduct of Family Studies
Ascertain “probands” (index cases) Define family (siblings? children? parents? grandparents?) Invite family members to participate Collect data (and, typically, biological samples) Copyright 2004 Jones and Bartlett Publishers

How to Select Control Families
Must decide how to identify controls. From spouse’s side of proband’s family? Or select a random sample from the population? Will controls be motivated to participate? Must take HIPAA rules into account. Copyright 2004 Jones and Bartlett Publishers

Analysis Issues Exclude the index cases and controls. Model disease (or behavior) of interest based on age, sex, known risk factors. Evaluate evidence for genetic effect through significance of variable(s) that indicate “relationship to index case.” Copyright 2004 Jones and Bartlett Publishers

Analysis Issues (cont’d)
Simplest “genetic” variable (1 if relative of case, 0 if relative of control). Can also construct indicator variables to designate type of relative. If not significant after including other risk factors, then no evidence for genetic influence. Copyright 2004 Jones and Bartlett Publishers

Evidence of genetic influence, so far….
Cases are more likely to have a family history of disease than controls. The excess risk to relatives is not accounted for by age, sex, and other risk factors. What does that tell us about the underlying genetic influence? (nothing) Copyright 2004 Jones and Bartlett Publishers

Other Approaches to Identify Genetic Influences
Twin studies Segregation analysis Linkage analysis Copyright 2004 Jones and Bartlett Publishers

Twin Studies A “natural experiment” of sorts. Monozygotic (MZ) twins are genetically identical. Dizygotic (DZ) twins share, on average, the same proportion of genes as siblings. Greater concordance (for dichotomous traits) or correlation (for continuous traits) for MZ than DZ twins is evidence of a genetic influence. Copyright 2004 Jones and Bartlett Publishers 9

Segregation Analysis Historically, linkage analysis required knowledge of the mode of transmission of the putative gene [dominant versus recessive, allele frequency, lifetime or age-specific risk (penetrance)]. Segregation analysis has been used to estimate these parameters. Copyright 2004 Jones and Bartlett Publishers

Linkage Analysis One way to distinguish cultural inheritance from genetic inheritance is to track a region of our DNA that is transmitted from parents to offspring in the same manner as the disease/outcome of interest. This procedure works well for diseases that follow simple rules of inheritance (e.g., autosomal dominant or recessive). Copyright 2004 Jones and Bartlett Publishers 10

Genetic Epidemiology of Complex Diseases
“Complex diseases” are ones for which the genetic influence may be modest and environmental factors contribute to disease risk. Segregation analysis is not typically done for “complex diseases.” Modern approaches ignore models of inheritance (non-parametric methods). Copyright 2004 Jones and Bartlett Publishers

Use of Epidemiology to Understand Genetic Variation
The methods of genetic epidemiology have been applied historically to identify genes. Typically, epidemiologists are not interested in mapping genes, but rather in figuring out how genes interact with environment to influence disease risk and outcome. Copyright 2004 Jones and Bartlett Publishers

Molecular Epidemiology
Related individuals are not necessarily required for studies of the association of genetic variation with risk of disease. Both cohort and case-control designs can be used. Because genetic code (germline DNA) is unchanged since conception, one readily can employ retrospective designs. Copyright 2004 Jones and Bartlett Publishers

Common Strategies for Genetic Marker Selection
Genome-wide approach with anonymous DNA markers (10,000 SNPs on a chip). SNPs or simple tandem repeat markers in “candidate” genes based on a priori knowledge about presumed function. SNP’s in candidate genes with known functional effect on level or activity of protein product. Copyright 2004 Jones and Bartlett Publishers

Primer on Single Nucleotide Polymorphisms (SNPs)
Because of our redundant genetic code, some SNP’s will not alter the encoded amino acid (e.g., GGA, GGG, GGT and GGC all encode proline). SNP’s that change an amino acid may not necessarily lead to change in function of transcribed protein. Copyright 2004 Jones and Bartlett Publishers

More on SNPs SNP’s that don’t change an amino acid may still lead to alternate splicing of the transcript (and therefore be functionally important). SNP’s in promoter region may influence level of protein product - not activity (and therefore be biologically significant). Copyright 2004 Jones and Bartlett Publishers

Caveats About SNP Studies
If you’re interested in gene x environment interactions--best to focus on SNPs with known functional effect. Human biology is complex: are alterations in one component of a pathway compensated for by another? Most SNPs are likely to be modest risk factors – requiring large sample sizes. Copyright 2004 Jones and Bartlett Publishers

Realistic Expectations
Almost every gene is modified after translation into protein (e.g., glycosylation, acetylation, methylation). Thus, the correlation between DNA sequence and protein is far from perfect. May be necessary to examine multiple SNPs within a gene and several genes within a pathway. 8 Copyright 2004 Jones and Bartlett Publishers

Molecular Epidemiology – Beyond Genetics
Biomarkers of exposure and disease extend beyond DNA. Viral or bacterial load. Morphometric analysis of tissues/cells. Hormone or lipid levels in blood or urine. Other examples? Copyright 2004 Jones and Bartlett Publishers

Conclusion Molecular and genetic epidemiology represent specialty areas of expertise. These specialty areas utilize and apply advances in molecular biology and molecular genetics of disease to: unravel disease etiology. enable novel approaches for early detection. inform more effective interventions by targeting those at greatest risk. Copyright 2004 Jones and Bartlett Publishers

CHAPTER 15 Psychologic, Behavioral, and Social Epidemiology

Learning Objectives, Abridged
State the role of psychologic, behavioral, and social factors in health and disease. Define status discrepancy, person-environment fit, and stressful life events. Discuss moderators of the stress-illness relationship. State outcomes of exposure to stress. Copyright 2004 Jones and Bartlett Publishers

Social Epidemiology: Definitions
Concerned with the influence of a person’s position in the social structure upon the development of disease (Syme, 1974). “ the branch of epidemiology that studies the social distribution and social determinants of states of health.” (Berkman, Kawachi, 2000) Copyright 2004 Jones and Bartlett Publishers

Behavioral Epidemiology
Studies the role of behavioral factors in health. Examples of behavioral factors are tobacco use, physical activity, and risky sexual behavior. Copyright 2004 Jones and Bartlett Publishers

Behavioral Medicine Related to behavioral epidemiology. Emphasizes the application of behavioral factors to specific clinical interventions, e.g., biobehavioral approaches to management of hypertension. Copyright 2004 Jones and Bartlett Publishers

Psychosocial Epidemiology
Broadly conceptualized term that includes psychological, behavioral, and social factors. Relevant to mental health states, e.g., grief and depression. Relevant to physical health states, e.g., chronic diseases. Copyright 2004 Jones and Bartlett Publishers

Guide to Psychosocial Epidemiology
Stress Social Incongruity Person- environment fit Life events Personality factors Type A behavior Culture Social support Lifestyle and Life and job dissatisfaction Mental health Depressive symptoms Independent Variables Moderating Variables Dependent Variables Copyright 2004 Jones and Bartlett Publishers

Research Designs Studies used in this field of investigation: Case-control Cohort Cross-sectional Needed are more: Longitudinal, prospective studies Studies of women and minority groups Valid and operationalized measures Copyright 2004 Jones and Bartlett Publishers

Example of Longitudinal, Prospective Study
The Early Stages of Psychopathology Study followed 3,021 adolescent and young adult residents of Munich, Germany. Begun in , subjects were followed up on average after a 42-month interval. Incidence of mental disorders examined. Copyright 2004 Jones and Bartlett Publishers

Social Context of Health
The social environment contributes to the regulation of psychosocial influences upon health. Example: In less developed areas, overcrowding, poor living conditions, and lack of preventive health care promote spread of infectious diseases. Copyright 2004 Jones and Bartlett Publishers

Global Burden of Disease Study
Assesses the worldwide consequences of disease. The disability-adjusted life year (DALY) combines information on mortality with information on morbidity for specific causes. Lower respiratory infections: leading global DALY. Copyright 2004 Jones and Bartlett Publishers

Independent Variables
General concepts of stress Social incongruity theory Person-environment fit Stressful life events Stress process model Copyright 2004 Jones and Bartlett Publishers

General Concepts of Stress: Canon
Canon studied changes in gastrointestinal function accompanying stressful events. Copyright 2004 Jones and Bartlett Publishers

General Concepts: Selye
Selye proposed that stress is a change in the environment of the organism. General adaptation syndrome specified three stages of response to stress: alarm reaction stage of resistance stage of exhaustion General adaptation syndrome associated with corticoid secretion. Copyright 2004 Jones and Bartlett Publishers

General Concepts: Crider
Crider proposed that adverse environmental events produce stress. Examples: noxious stimuli removal of reinforcement conflict situation The executive monkey experiments demonstrated physiological effects (e.g., gastric ulcers) associated with stress. Copyright 2004 Jones and Bartlett Publishers

Social Incongruity Theory
The guiding hypothesis is that either social mobility or status incongruity may be associated with morbidity. Themes of research are correlates of changes in residence; intragenerational mobility; husband-wife discrepancy in status. Copyright 2004 Jones and Bartlett Publishers

Social Incongruity Theory (cont’d)
Cobb, et al. (1969) examined discrepancy between husband and wife in social and educational status as associated with arthritis. Syme, et al. (1966) studied the association between cultural mobillity and coronary heart disease. Copyright 2004 Jones and Bartlett Publishers

Person-Environment Fit Model
“conceives of adjustment as the goodness of fit between the characteristics of the person and the properties of [his or her] environment.” (French, et al., 1974) Lack of adjustment occurs when there are discrepancies between demands from the environment and supplies (resources) to meet those demands. Copyright 2004 Jones and Bartlett Publishers

Social Readjustment Rating Scale
Holmes and Rahe (1967) developed 43-item Social Readjustment Rating Scale. Each item represented a life event. The more severe the life change event and the higher the frequency of the event, the greater the chance that severe disease will occur. Copyright 2004 Jones and Bartlett Publishers

Ten Leading Life Change Events
death of a spouse divorce marital separation jail term death of a close family member personal injury or illness marriage being fired from a job marital reconciliation retirement Copyright 2004 Jones and Bartlett Publishers

Pearlin’s Stress Process Model
Used as a guide for stress research. Stress: a process occurring over time. Events chain from one another with interconnectedness among various factors: social and economic status life events and chronic strains moderating resources, e.g., coping skills stress outcomes, e.g., mental disorders Copyright 2004 Jones and Bartlett Publishers

Moderating Factors in the Stress-Illness Relationship
Type A behavior pattern Social support Personal behavior, lifestyle, and health Copyright 2004 Jones and Bartlett Publishers

Type A (Coronary-Prone) Behavior Pattern
Found to be associated with CHD. Characteristics include aggressiveness, ambition, drive, and competitiveness. Interview measure and self-administered measure used. Copyright 2004 Jones and Bartlett Publishers

Social Support Refers to perceived emotional support that one receives from social relationships. Operates as mediator--buffers against stress. May enhance immune status. Lack of social support may contribute to onset and severity of psychological stress. Copyright 2004 Jones and Bartlett Publishers

Social Network Ties Quantitative concept that refers to the number (and patterns) of ties that one has with other people and organizations. May serve to lessen the adverse psychologic consequences of stress and reduce levels of depression. Copyright 2004 Jones and Bartlett Publishers

Social Network Ties: Example
Marital status is related to the types of social network ties maintained. Married older adults have more contact with family members than with friends and receive more emotional support than unmarried older adults. Copyright 2004 Jones and Bartlett Publishers

Personal Behavior, Lifestyle, and Health
Healthy People 2000 is a document that established a framework in the U.S. for national health promotion and disease prevention objectives. Health promotion priority activities include physical activity and fitness, nutrition, and reduction of tobacco use. Copyright 2004 Jones and Bartlett Publishers

The Alameda County Study (Breslow)
Seven healthful habits: moderate food intake eating regularly eating breakfast not smoking cigarettes moderate or no use of alcohol moderate exercise 7 to 8 hours of sleep daily Copyright 2004 Jones and Bartlett Publishers

Health-Related Aspects of Personal Behavior
risk taking sexual behavior dietary practices and exercise levels smoking alcohol consumption choice of occupation Copyright 2004 Jones and Bartlett Publishers

Smoking and Health Overall 70% excess morbidity among smokers compared to nonsmokers. Mortality from smoking increases with quantity of cigarettes smoked. Association between smoking and cardiovascular diseases, cancer, pulmonary diseases, peptic ulcer disease. Copyright 2004 Jones and Bartlett Publishers

Alcohol Consumption Excessive consumption is a risk factor for cirrhosis, peptic ulcers, gastritis. Increases likelihood of motor vehicle accidents. Deterioration of family environment and job loss. Fetal alcohol syndrome. Copyright 2004 Jones and Bartlett Publishers

Dietary Practices Association between consumption of refined carbohydrate foods and obesity and diabetes. Lack of dietary fiber related to diseases of the bowel. Consumption of saturated fats and cholesterol associated with arteriosclerosis and heart disease. Copyright 2004 Jones and Bartlett Publishers

Sedentary Lifestyle Risk factor for CHD and other conditions. Morris, et al. (1973) found vigorous exercise, not light exercise, reduced incidence of CHD. Paffenbarger, et al. (1978) corroborated findings for vigorous exercise. Copyright 2004 Jones and Bartlett Publishers

Sociocultural Influences on Health
Culture is defined as the set of values to which a group of people subscribes, as the way of life of a group of people, or as the totality of what is learned and shared through interaction of the members of a society. Copyright 2004 Jones and Bartlett Publishers

CHD in Japanese Men: Marmot, et al. (1975)
Compared CHD rates among men of Japanese ancestry living in Japan, Honolulu, and San Francisco. Rates lowest in Japan, highest in San Francisco, intermediate in Honolulu. Possibly due to variations between the two countries in terms of diet, occupation, and the social and cultural milieu. Copyright 2004 Jones and Bartlett Publishers

Utilization of Health Services
Preference for health care services varies according to cultural background. Persons from traditional cultures may prefer folk medicine and family care. Persons from more developed societies may prefer technologically advanced medical services. Copyright 2004 Jones and Bartlett Publishers

Outcome Variables These include physical health, mental health, and affective states. Some topics covered are: Life and job dissatisfaction. Mental health and stressors. Premorbid psychologic factors and cancer. Copyright 2004 Jones and Bartlett Publishers

Life and Job Dissatisfaction
Sales and House (1971) demonstrated a strong negative correlation between job satisfaction and coronary disease death rates. Copyright 2004 Jones and Bartlett Publishers

Dissatisfaction (cont’d)
Tedious work, feeling ill at ease at work, lack of recognition, difficulties with coworkers, demotion, and prolonged emotional strain associated with work overload have been shown to be related to coronary disease. Copyright 2004 Jones and Bartlett Publishers

Mental Health and Stressors
Epidemiologic research has examined psychologic disorders and affective states as outcomes of stress-illness paradigm. Psychologic disorders: posttraumatic stress disorder and major depression. Affective states: depressive symptoms. Copyright 2004 Jones and Bartlett Publishers

Depression: Frerichs, et al. (1982)
Prevalence of depression in a representative sample of adults in Los Angeles County was 19%. Rates of depression among women higher than men (23.5% vs. 12.9%). Depressed persons reported more physical illness than nondepressed. Copyright 2004 Jones and Bartlett Publishers

Cancer: Psychologic Factors
Fox (1978)--two major personality types at increased risk of cancer: Yielding, compliant, eager to please. Extroverted, nonneurotic individuals who tend toward heaviness. Fox’s 1995 review showed contradictory findings regarding psychologic variables and cancer. Copyright 2004 Jones and Bartlett Publishers

Effects of Major Diseases on Personality
Severe illness may bring about personality changes in the individual, spouse, children, and coworkers. Wives of heart attack victims experience depression, fear, anxiety, and guilt. Heart attack victims may experience similar feelings. Copyright 2004 Jones and Bartlett Publishers

Personality and Smoking: Surgeon General’s Report (1979)
Personality factors related to smoking behavior may include extroversion, neuroticism, antisocial tendencies, and belief that one is externally controlled. Smokers may show greater risk-taking, impulsiveness, and interest in sex. Copyright 2004 Jones and Bartlett Publishers

Habitual Mental Outlook and Health Status
Habitual mental outlook includes mental health, adult adjustment, cheerfulness, and sense of humor. Valliant (1979) demonstrated association between good mental health and physical health. Results of other studies inconsistent. Copyright 2004 Jones and Bartlett Publishers

Chapter 1 The History and Scope of Epidemiology.

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Chapter 1 The History and Scope of Epidemiology.

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