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An Overview of Analytic Epidemiology A link between antecedent factors and Association some outcome –possibly a causal relationship, but not necessarily. Exposure Outcome (Risk Factor) Outcomes Exposures Dependent variable “Risk factors” Disease occurrence Preventive measures Management strategy Independent variables Examples: Lack of exercise Heart disease? Flu Shot Dystonia Disorder? Evolution of Information Descriptive Case Report Studies Case-Series Description; Hypothesis Generation Cross-Sectional Correlational Hypothesis testing Analytical Compare groups Studies Case-Control Observational Cohort Study Comparison Studies Clinical Trial Evaluation of Intervention (Intervention Study) In analytic studies one enrolls subjects from a population and groups them in some way to make comparisons that test association between risk factors and outcomes. Target Population Inference Sample Study Are the results valid? Population Chance Bias Confounding • Collect data Is there an association? • Make comparisons Two Basic Strategies for Testing Associations • Cohort type of study • Case-Control study Exposed Cohort X X Type X Studies Compare Time passes Incidence X Non-Exposed X XX X Case-Control XX X Diseased Studies Compare Compare odds of Prior exposure to risk factor Exposures Non-Diseased A Salmonella Outbreak Surveillance system for reportable infectious diseases identifies a case of Salmonella food poisoning. Subsequent surveillance and active case finding revealed a substantial number of recent cases. Local High School Based on the descriptive epidemiology, it is clear that the parent-teacher luncheon is the source of the outbreak (presumably one of the food dishes). But which food dish was responsible? An Intuitive Approach The attendees of the luncheon constitute a well-defined group (cohort) that is the “source population.” Any of a number of food dishes could have been the “exposure” responsible for causing Salmonella in some members of the cohort. An intuitive approach would be to ask all attendees in the cohort what they ate (their exposures). Then, for each food dish sort the attendees into those who ate it and those who did not, and then compare the incidence of Salmonellosis (the outcome) in the two exposure groups.
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