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Study Designs for Analytic Epidemiology

Study Designs for Analytic Epidemiology. Session 3, Part 2. Learning Objectives Session 3, Part 2. Define analytic epidemiology List 3 types of observational study designs. Overview Session 3, Part 2. Review of descriptive vs. analytic epidemiology Components of analytic epidemiology

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Study Designs for Analytic Epidemiology

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  1. Study Designs for Analytic Epidemiology Session 3, Part 2

  2. Learning ObjectivesSession 3, Part 2 • Define analytic epidemiology • List 3 types of observational study designs

  3. OverviewSession 3, Part 2 • Review of descriptive vs. analytic epidemiology • Components of analytic epidemiology • Types of analytic study designs

  4. Descriptive versus Analytic Epidemiology

  5. Descriptive vs. Analytic Epidemiology

  6. Analytic Epidemiology • Used to help identify the cause of disease • Typically involves designing a study to test one or more hypotheses

  7. Source: Borgman, J (1997). The Cincinnati Enquirer. King Features Syndicate.

  8. Components of Analytic Epidemiology

  9. Exposure and Outcome • Exposure: Any factor that might influence one’s risk of disease • Outcome: Disease or condition, standardized using case definitions

  10. Case Definition • Standard diagnostic criteria that must be fulfilled to identify a person as a case of a particular disease • Clinical (laboratory results, symptoms, signs) • Restrictions on person, place, and time • Ensures that all persons who are counted as cases actually have the same disease

  11. Developing Hypotheses • A hypothesis is an educated guess about an association that is testable in a scientific investigation • Descriptive data provide information to develop hypotheses • Hypotheses tend to be broad initially and are then refined to have a narrower focus

  12. Hypothesis Example • Hypothesis: People who ate at the church picnic were more likely to become ill • Exposure is eating at the church picnic • Outcome is illness – this would need to be defined, for example, ill persons are those who have diarrhea and fever

  13. Hypothesis Example • Hypothesis: People who ate at the church picnic were more likely to become ill • Exposure is eating at the church picnic • Outcome is illness – this would need to be defined, for example, ill persons are those who have diarrhea and fever • Hypothesis: People who ate the egg salad at the church picnic were more likely to have laboratory-confirmed Salmonella • Exposure is eating egg salad at the church picnic • Outcome is laboratory confirmation of Salmonella

  14. Types of Analytic Studies

  15. Main Categories of Studies • Experimental studies – exposure status is assigned by investigators • Observational studies – exposure status is not assigned

  16. Experimental Studies • Can involve individuals or communities • Assignment of exposure status can be random or non-random • The non-exposed group can be untreated, untreated with placebo, or given a standard treatment • Most common design is a randomized clinical trial

  17. Experimental Study Examples • Randomized clinical trial to determine if giving magnesium sulfate to pregnant women in preterm labor decreases the risk of their babies developing cerebral palsy • Randomized community trial to determine if fluoridation of the public water supply decreases dental cavities

  18. Observational Studies • Three main study designs: • Cross-sectional study • Cohort study • Case-control study

  19. Cross-Sectional Studies • Exposure and outcome status are determined at the same time • “Snapshot” • Examples include: • Behavioral Risk Factor Surveillance System (BRFSS) http://www.cdc.gov/brfss/ • National Health and Nutrition Surveys (NHANES) http://www.cdc.gov/nchs/nhanes.htm • Also include most opinion and political polls

  20. Cohort Study Description • Study population is grouped by exposure status • Groups are then followed to determine if they develop the outcome

  21. Cohort Study Design Study Population Exposure is self selected Non-exposed Exposed

  22. Cohort Study Design Study Population Exposure is self selected Non-exposed Exposed Follow through time Disease No Disease Disease No Disease

  23. Cohort Study Examples • Study to determine if those exposed to environmental tobacco smoke (ETS) have a higher risk of leukemia than those not exposed to ETS • Study to determine if children who receive influenza vaccination miss fewer days of school than those who did not receive it • Study to determine if the egg salad was the cause of a foodborne illness outbreak

  24. Case-Control Study Description • Study population is grouped by outcome • Cases are persons who have the outcome • Controls are persons who do not have the outcome • Past exposure status is then determined

  25. Case-Control Study Design Study Population Select based on disease status Controls Cases

  26. Case-Control Study Design Study Population Select based on disease status Controls Cases Look back in time Had Exposure No Exposure Had Exposure No Exposure

  27. Case-Control Study Examples • Study to determine whether women with strokes had hormone replacement therapy as compared to women without strokes • Study to determine whether lung cancer patients have more radon exposure than non-lung cancer controls • Study to determine whether salmonella infection was associated with eating at a fast food restaurant

  28. Cohort versus Case-Control Study

  29. Summary • Analytic epidemiology addresses “why” and “how” a health problem occurs • In experimental studies investigators assign exposures to study participants • In observational studies investigators observe exposures and outcomes that are already occurring in the population • Commonly used observational study designs are cohort studies and case-control studies

  30. References and Resources • Centers for Disease Control and Prevention. Principles of Epidemiology. 3rd ed. Atlanta, Ga: Epidemiology Program Office, Public Health Practice Program Office; 1992. • Gordis L. Epidemiology. 2nd ed. Philadelphia, Pa: WB Saunders Company; 2000. • Gregg MB, ed. Field Epidemiology. 2nd ed. New York, NY: Oxford University Press; 2002. • Hennekens CH, Buring JE. Epidemiology in Medicine. Philadelphia, Pa: Lippincott Williams & Wilkins; 1987. • Cohort Studies. ERIC Notebook [serial online]. 1999:1(3). Department of Epidemiology, University of North Carolina at Chapel Hill School of Public Health / Epidemiologic Research & Information Center, Veterans Administration Medical Center. Available at: http://cphp.sph.unc.edu/trainingpackages/ERIC/issue3.htm. Accessed March 1, 2012.

  31. References and Resources • Case-Control Studies. ERIC Notebook [serial online]. 1999:1(5). Department of Epidemiology, University of North Carolina at Chapel Hill School of Public Health / Epidemiologic Research & Information Center, Veterans Administration Medical Center. Available at: http://cphp.sph.unc.edu/trainingpackages/ERIC/issue5.htm. Accessed March 1, 2012. • Laboratory Instructor’s Guide: Analytic Study Designs. EPID 168 Lecture Series. Department of Epidemiology, University of North Carolina at Chapel Hill School of Public Health; August 2002. Available at: http://www.epidemiolog.net/epid168/labs/AnalyticStudExerInstGuid2000.pdf. Accessed March 1, 2012.

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