Population Health for Health Professionals

Module 2 Epidemiology The Basic Science of Public Health

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

Part I Key Terms and Measures

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

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

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

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

Three Essential Components l Disease distribution l Disease determinants l Disease frequency s Expected level s Endemic s Sporadic s Epidemic s Pandemic

Epidemiologic Studies l Descriptive l Analytic

Descriptive Studies l Frequency of occurrence of particular condition l Patterns of occurrence according to person, place and time

Analytic Studies l Observational studies s case-control studies s cohort studies u prospective u retrospective l Experimental studies

Case Control Study Key Basis for selection of group for study = present = absent ExposureDisease ? ?

Key Basis for selection of group for study = present= absent Prospective Cohort Study ? ? ExposureDisease

Retrospective Cohort Study Key Basis of selection of group for study = present = absent ? ? ExposureDisease

Analytic Studies l Observational studies l Experimental studies s Intervention studies s Clinical trials

Basic Presentation of Results All rates and ratios discussed can be calculated from this.

Smoking and Carcinoma of the Lung

Interpreting Results: Measurement Errors l Bias s information s selection l Confounding s extraneous factors l Effect modification s statistical interaction

Interpreting Results: Cause- Effect Relationship l Strength of the association l Consistency l Temporality l Plausibility l Biological gradient

Measures of Disease Frequency l Prevalence l Incidence

Prevalence l Prevalence= number of existing cases divided by total population s Visual examination survey 310 X 100 = 12.5% 2477

Types of Prevalence Measures

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%

Types of Incidence Measures

Rates Commonly Used in Epidemiology l Crude l Category specific l Age adjusted

Module Author Fran C. Wheeler, Ph.D School of Public Health University of South Carolina