1.   Epidemiology

2. Classically speaking Epi = upon (among) Demos = people Ology = science
Epidemiology = the science which deals with what falls upon people…..

3. A Modern Definition
“The study of the distribution and determinants of health-related states in specified populations, and the application of this study to control health problems."
(Last J)
Search for knowledge Apply in health service

4. Objectives of Epidemiology
1. To describe the distribution and magnitude of health and disease problems in the population.
2. To identify the etiological factors – risk factors in the population.
3. To provide the data essential to planning, implementation and evaluation of services for prevention, control and treatment of disease and to setting up of priorities for these services.

5. The ultimate aim of epidemiology is
to eliminate or reduce health problem or its consequences
and
to promote health and well-being of society as a whole.

6. Purposes of Epidemiology
To investigate nature / extent of health-related phenomena in the community / identify priorities
To study natural history and prognosis of health-related problems
To identify causes and risk factors
To recommend / assist in application of / evaluate best interventions (preventive and therapeutic measures)
To provide foundation for public policy 6

7. Component: Disease Frequency- Rate and Ratio e.g
Rate- incidence rate, prevalence rate etc
Ratio- sex ratio, doctor-population ratio
Distribution of Disease-
Disease in community find causative factor
Generate hypothesis
Descriptive epidimiology

8. Determinants of Disease-
To test hypothesis
Analytic epidemiology
Help in develop sound scientific program

9. Incidence
Number of new cases of a disease which come into being during a specified period of time.
(Number of new cases of specific disease during a given period)/(population at risk during that period) x 1000
Importance: If incidence increasing, it may indicate failure or ineffectiveness of control measure of a disease and need for better/new health control measure.

10. Prevalence
Number of current case (old and new) of a specified disease at a point of time
It help to estimate the burden of disease
Identify potentially high-risk populations. They are essentially helpful to plan rehabilitation facilities, manpower needs, etc.
(Number of current case of a specified disease at a point of time)/(estimated population at the same point of time) x 100
Point prevalence AND Period prevalence

11. Relationship between incidence and prevalence
Prevalence =Incidence x Duration

12. Approach of an epidemiologist
Asking questions
making comparisons
● Asking questions may provide clues to cause or aetiology of disease e.g.
What is the event,
what is its magnitude,
where did it happen,
when did it happen,
who were affected,
why did it happen?

13. Making comparisons will help draw inferences to support asking questions.
This comparison may be:
● Between those with the disease and those without the disease;
● Those with risk factor and those not exposed to risk factor;

14. Terms to know
Endemic: constant presence of a disease in a given population
epidemic: outbreak or occurrence of one specific disease from a single source, in a group population, community, or geographical area, in excess of the usual level of expectancy
pandemic: epidemic that is widespread across a country, or large population, possible worldwide

15. Epidemiology versus clinical medicine
Unit of study is case
Concerned with only sick
Patient comes to doctor
Seeks diagnosis, derives prognosis, prescribes specific treatment
Unit of study is a defined population or population at risk
Concerned with sick as well as healthy
Investigator goes to the community
identify source of infection, mode of spread, an Etiological factor, future trend or recommend control measures

16. Host Agent Environment
Three essential characteristics that are examined to study the cause(s) for disease in analytic epidemiology are...
Host
Agent
Environment

18. Host Factors Behaviors Genetic predisposition Immunologic factors
Influence the chance for disease or its severity

19. Agents
Biological
Physical
Chemical
Necessary for disease to occur

20. Environment
External conditions
Contribute to the disease process

21. Due to change in number of susceptibles in the population
Epidemics arise when host, agent, and environmental factors are not in balance
Due to new agent
Due to change in existing agent (infectivity, pathogenicity, virulence)
Due to change in number of susceptibles in the population
Due to environmental changes that affect transmission of the agent or growth of the agent

22. EPIDEMIOLOGICAL METHODS.
The methods he employs can be classified as:
1. Observational studies
a. Descriptive studies
b. Analytical studies
– Case control studies
– Cohort studies
2. Experimental/interventional studies
– Randomized control studies
– Field trials
– Community trials

23. Descriptive observations pertain to the “who, what, where and when of health-related state occurrence”. However, analytical observations deal more with the ‘how’ of a health-related event occur.
Randomized control trial (often used for new medicine or drug testing), field trial (conducted on those at a high risk of conducting a disease), and community trial (research on social originating diseases)

24. Descriptive Studies
Steps in conducting a descriptive study.
Descriptive studies form the first step in any process of investigation.
These studies are concerned with observing the distribution of disease in populations.
1. Defining the population.
2. Defining disease under study.
3. Describing the disease.
4. Measurement of disease
5. Compare
6. Formulate hypothesis-

25. Defining the population
Defining the population. Defined population may be the whole population or a representative sample.
It can also be specially selected group such as age and sex groups, occupational groups, hospital patients, school children, small community, etc.

26. 2. Defining disease under study.
3. Describing the disease.
Disease is examined by the epidemiologist by asking three questions:
● When is the disease occurring—time distribution?
● Where is it occurring—place distribution?
● Who is getting the disease—person distribution?

27. A. Time Distribution
Short-term fluctuations.
Common source epidemics
- single exposure/point source—bhopal tragedy
Propagated-infectious :Hep A
Periodic fluctuations;
Seasonal –measles (early spring)
cyclic ,, in pre-vaccinated era (peak 2-3 yr)
Long-term or secular trends; diabetes, CVD

28. B. Place Distribution
International variations:
Cancer of stomach very common in Japan
less common in US.
oral cancer- India
Breast cancer- Low-japan, high-western
National variations, e.g. Distribution of fluorosis,

29. Rural-urban differences, e.g.
CVD, Mental illness more common in urban areas.
Skin diseases, worm infestations more common in rural areas.
Local distributions, e.g. Spot maps- John Snow in London to incriminate water supply as cause of cholera transmission in London.

30. cholera cases in proximity to water pump, 1854

32. C. Person Distribution
Age: e.g.
Measles is common in children,
Cancer in middle age
Degenerative diseases in old age.
Sex:
Women- Lung cancer-less
Hyperthyroidism- more
c. Social class- Diabetes, Hypertenson– upper class

33. 4. Measurement of disease- Mortality/ Morbidity
5. Compare- Between different population, subgroups
6. Formulate hypothesis. On basis of all data epidemiologist form hypothesis.

34. Cross-sectional studies
Cross-sectional study is also called prevalence study.
Cross-sectional study is the simplest form of observational study.
It is based on single examination of cross-section of population at one point of time.
If the sampling methodology is accurate, results can be projected to the entire population.
They are more useful for chronic illnesses, e.g. hypertension.
Cross-sectional studies save on time and resources, but provide very little information about natural history of disease and incidence of illness.

35. Case- control studies
It start from effect and then proceed to cause
Both exposure and outcome have occurred before start of the study
The study proceeds backwards from effect to cause

36. Select subjects based on their disease status.
A group of individuals that are disease positive (the "case" group) is compared with a group of disease negative individuals (the "control" group).
The control group should ideally come from the same population that gave rise to the cases.

37. Basic steps in a case-control study
1. Selection of cases and controls
2. Matching
3. Measurement of exposure
4. Analysis and interpretation.

38. A 2×2 table is constructed, displaying exposed cases (A), exposed controls (B), unexposed cases (C) and unexposed controls (D).
To measure association is the odds ratio (OR), which is the ratio of the odds of exposure in the cases (A/C) to the odds of exposure in the controls (B/D), i.e.
OR = (AD/BC).
CASE
CONTROLS
EXPOSED A B
UNEXPOSED C D

39. Case with lung cancer
Control without lung cancer
Smokers (less than 5 )
33 (a)
55 (b)
Non-Smokers (less than 5 )
2 (c)
27 (d)
The first step is to find out
1. Exposure rates among cases
=a/(ac) = 33/35 =94.2%
2. Exposure rate among the controls
=b/(bd) = 55/82 =67%

40. If the exposure rate among the cases is more than the controls.
We must see if the exposure rate among the cases is significantly more than the controls. This is done by using the chi-square test
It is significant if p is less than 0.05.

41. Odds ratio
It is a measure of strength of association between the risk factor and outcome.
The derivation of the odds ratio is based on three assumptions:
● The disease being investigated is relatively rare
● The cases must be representative of those with the disease
● The controls must be representative of those without the disease.

42. Odds ratio a.d/b.c
33X27/55X2 = 8.1
People who smoke less than 5 cigarettes per day showed a risk of having lung cancer 8.1 times higher as compared to non-smokers.

43. OR is > 1- "those with the disease are more likely to have been exposed,"
OR close to 1 then the exposure and disease are not likely associated.
OR <1-exposure is a protective factor in the causation of the disease.

44. Case control studies are usually faster and more cost effective
Sensitive to bias (selection bias).
The main challenge is to identify the appropriate control group;
The distribution of exposure among the control group should be representative of the distribution in the population that gave rise to the cases.

45. Cohort Study It look at cause and proceed to effect
study before the disease is manifest and proceed to study over a period of time for the disease to occur.
Cohort means a group of people sharing a common experience.
Cohort studies are often prospective studies, they can be retrospective also, or a combination of both prospective and retrospective components can be brought in.

46. Steps in a cohort study:
Selection of study subjects
Obtaining data on exposure
Selection of comparison groups
Follow-up
Analysis.

47. CHD Develop
CHD does not develop
total
Smoker
84 (a)
2916 (b)
3000 (a+b)
Non-smoker
87 (C)
4913 (d)
5000 (c+d)
Total
171 (a+c)
7829 (b+d)
8000
The incidence rates of CHD among smokers i.e. a/(a+b)
=84/ =28 per 1000
The incidence rates of CHD among non-smokers i.e =c/(c+d)
=87/ =17.4 per 1000

48. Then, we must determine if the incidence rate among the smokers is significantly more than among the non-smokers by using the chi-square test.

49. Relative risk (RR)
It is ratio of incidence of the disease among the exposed and incidence among the non-exposed.
RR (incidence of disease among exposed)/
(Incidence of disease among non-exposed)
=a/(ab)/c/(cd)
=28/17.4
=1.6
If RR is more than 1, then there is a positive association
If RR is equal to 1, then there is no association
Smokers develop CHD 1.6 times more than nonsmokers.

50. Attributable risk (AR)
This is defined as amount or proportion of disease incidence that can be attributed to a specific exposure.
It indicates to what extent the disease under study can be attributed to the exposure:
(incidence of disease among exposed)
- (incidence of disease among non exposed)/
(Incidence of disease among exposed)
= /28
= 10.6/28 = = 37.9%
37. 9% of CHD among the smokers was due to smoking.

51. Differences between case-control and cohort studies
Case-control Cohort studies
Proceeds from effect to ● Proceeds from cause to
cause effect
Starts with the disease ● Starts with people exposed to risk factor
Rate of exposure among ● Tests frequency of disease
exposed and those not among those exposed and exposed is studied those not exposed
First approach to testing ● Reserved for testing
hypothesis precisely define hypothesis

52. Involves small number of ● Involves large number of
subjects subjects
Less time and resources ● More time and cost
intensive
Suitable for rare diseases ● Difficult to conduct for rare
diseases
Yields odds ratio ● Yields incidence rates,
RR, AR and population atributable risk
Cannot yield information ● Information about more
about diseases one other than disease is possible
than selected for

53. Randomized Control Studies
Essential elements are:
Drawing up a strict protocol,
selecting reference and experimental populations,
randomization,
intervention,
follow-up
assessment of outcome.

54. Randomization is a statistical procedure where participants are allocated into groups called study and control groups to receive or not to receive an experimental therapeutic or preventive procedure, intervention.
Randomization is an attempt to avoid bias and allow comparability.

55. Study designs include
Concurrent parallel
Crossover type of study designs.
In the former, study and control groups will be studied parallel whereas in the latter all the participants will have the benefit of treatment after a particular period because the control group becomes study group.

56. Types of randomized control studies are:
Clinical trials, e.g. drug trials
Preventive trials, e.g. trials of vaccines
Risk factor trials, e.g. trials of risk factors of cardiovascular disease, e.g. tobacco use, physical activity, diet, etc.
Cessation experiments, e.g. smoking cessation experiments for studying lung cancer.

57. What is bias? Bias is systematic error that comes in.
Bias on the part of participants if they know they belong to study group—participant bias
bias because of observer if he knows that he is dealing with study group—observer bias
bias because of investigator investigator bias, if he knows he is dealing with study group.
In order to prevent this, a technique called blinding is adopted.

58. Concept of blinding
Single blind trial means participant will not know whether he belongs to study group or control group.
In double blind studies, both the participant and the observer will not be aware.
In triple blind study, the participant, observer as well as the investigator will not be aware

59. Efforts to detect cancer before symptoms appear
SCREENING
Active search for apparently healthy people is called
screening.
It is defined as search for unrecognized disease or defect by rapidly applied tests, examinations or other procedures in apparently healthy individuals.
Basic purpose of screening is to sort out from a large group of apparently healthy individuals—those likely to have disease, bring those apparently abnormal under medical supervision and treatment.
Efforts to detect cancer before symptoms appear

60. Four main uses of screening are:
(i) case detection,
(ii) control of spread of infectious diseases
(iii) research purposes especially for studying the natural history of chronic diseases
(iv) screening programs have lot of opportunities to educate people.

61. Iceberg phenomenon of a disease explains progress of disease from subclinical stages to overt manifestation.
Floating tips represent what the dental surgeon see and hidden portion represents unrecognized disease. Its detection and control are challenges.

62. Iceberg phenomenon of a disease explains progress of disease from subclinical stages to overt manifestation.
Floating tips represent what the dental surgeon see and hidden portion represents unrecognized disease. Its detection and control are challenges.

63. Q-1 Incidence of any disease can be known by: A. Longitudinal study.
B. Cross-sectional study.
C. Retrospective study.
D. Case control study.
ANS: A

64. Q-2
A study in which a particular individual is studied at different age is called as:
A. Retrospective study
B. Prospective study
C. Cross sectional study
D. Longitudinal study
Ans:D

65. Q-3
When planning of the entire study is completed before data is collected and analysed is cosidered as:
A. Retrospective study
B. Prospective study
C. Cross sectional study
D. Longitudinal study
Ans:B

66. Q-4 Case control study is a part of: A. Descriptive epidemiology
B. Experimental epidemiology
C. Analytical epidemiology
D. Serological epidemiology
Ans: c

67. Odds ratio (OR) of getting oral cancer in gutka chewers is: 0.44 1.0
Q-5
Cases
(Oral cancer )
Control
(with out oral cancer)
Gutka chewer
20 (a)
15 (b)
Non Gutka chewer
15 (c)
20 (d)
Odds ratio (OR) of getting oral cancer in gutka chewers is:
0.44
1.0
1.7
2.5
Ans: C

68. Q-6 Hypothesis is: A. A report. B. A synopsis. C. A theory.
D. A supposition from an observation.
ANS: D

69. Q-7
Relationship of prevalence (P), incidence (I) & duration (D) in epidemiology
I=PD
P=ID
D=PI
none
Ans: b

70. Q-8 Constant presence of a disease in a given population Endemic
Pandemic
Epidemic
Sporadic
Ans: a

71. Q-9
Which one is not the step of descriptive study a. Describing the disease. 4. Measurement of disease 5. Blinding 6. Formulate hypothesis
Ans: c

72. Q-10 In descriptive epidemiology, Describing the disease in all except
a. When is the disease occurring
b. Where is it occurring
c. Who is getting the disease
d. How is the disease occure
Ans: d