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Population Health for Health Professionals
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Module 2 Epidemiology The Basic Science of Public Health
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OBJECTIVES l epidemiology and role as foundation for public health l common measures of disease frequency l strengths and weaknesses of study designs l applications of epidemiologic method
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Part I Key Terms and Measures
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Epidemiology l Study of distribution of determinants and antecedents of health and disease in human populations l Application of results to control of health problems
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From Hippocrates to John Graunt l Fifth century BCE, Hippocrates pointed to the need to understand the environment and the risks it posed to understand the experience of disease l 1662, John Graunt analyzed weekly reports of births and deaths in London, quantifying patterns of disease in the population
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From William Farr to John Snow l 200 years later, Dr. William Farr was made responsible for medical statistics in the Office of the Registrar General for England and Wales l A mere 20 years later, John Snow completed his study of cholera
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Modern Experiences l Evaluation of risk factors for chronic diseases using case controls l Long term population studies using cohorts l Design of clinical trials to evaluate interventions
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Three Essential Components l Disease distribution l Disease determinants l Disease frequency s Expected level s Endemic s Sporadic s Epidemic s Pandemic
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Epidemiologic Studies l Descriptive l Analytic
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Descriptive Studies l Frequency of occurrence of particular condition l Patterns of occurrence according to person, place and time
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Analytic Studies l Observational studies s case-control studies s cohort studies u prospective u retrospective l Experimental studies
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Case Control Study Key Basis for selection of group for study = present = absent ExposureDisease ? ?
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Key Basis for selection of group for study = present= absent Prospective Cohort Study ? ? ExposureDisease
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Retrospective Cohort Study Key Basis of selection of group for study = present = absent ? ? ExposureDisease
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Analytic Studies l Observational studies l Experimental studies s Intervention studies s Clinical trials
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Basic Presentation of Results All rates and ratios discussed can be calculated from this.
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Smoking and Carcinoma of the Lung
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Interpreting Results: Measurement Errors l Bias s information s selection l Confounding s extraneous factors l Effect modification s statistical interaction
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Interpreting Results: Cause- Effect Relationship l Strength of the association l Consistency l Temporality l Plausibility l Biological gradient
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Measures of Disease Frequency l Prevalence l Incidence
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Prevalence l Prevalence= number of existing cases divided by total population s Visual examination survey 310 X 100 = 12.5% 2477
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Types of Prevalence Measures
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Incidence l Incidence = number of new cases in a given period of time divided by the total population at risk s Bacteremia among contraceptive users u 27/483 X 100 = 5.6%
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Types of Incidence Measures
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Rates Commonly Used in Epidemiology l Crude l Category specific l Age adjusted
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Module Author Fran C. Wheeler, Ph.D School of Public Health University of South Carolina
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