05-InterventionStudies

05-InterventionStudies - Principles of Epidemiology for...

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2/8/2011 Intervention studies 1 Study designs: Intervention trials Principles of Epidemiology for Public Health (EPID600) Victor J. Schoenbach, PhD www.unc.edu/~vschoenb Department of Epidemiology Gillings School of Global Public Health University of North Carolina at Chapel Hill www.unc.edu/epid600/
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9/24/2001 2 On inspiration A boy was watching his father, a pastor, write a sermon. “How do you know what to say?” he asked. “Why, God tells me.” “Oh, then why do you keep crossing things out?”
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2/8/2011 Intervention studies 3 Topics for this lecture Causality - the counterfactual model Experimental and observational epidemiologic study designs Types of intervention trials Methodological issues Ethical issues
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2/8/2011 Intervention studies 4 Causality - the counterfactual model How do we discover causation? Toddler playing with a lamp switch Causation is not observed but inferred Conceptual models, assumptions, and reference frames underlie causal inference
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1/6/2002 Intervention studies 5 Counterfactual model for causal inference in “modern epidemiology” Compare the outcome in “ exposed ” group to what the outcome would have been if had not been exposed Compare the outcome in “ unexposed ” group to what the outcome would have been if had been exposed These comparisons are counterfactual
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1/6/2002 Intervention studies 6 In practice: use a substitute population Since can’t compare to counterfactual, compare the outcome for the “ exposed ” group to the outcome in a “ substitute population Substitute population represents the “exposed group without the exposure”. Validity of inference depends on finding a valid substitute population
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2/8/2011 Intervention studies 7 Experimental and observational studies Analytic epidemiologic studies compare “exposed” to “unexposed” groups, but epidemiologists usually observe exposures rather than assign them. In experimental (intervention) studies, the researcher determines who is exposed . Most epidemiologic studies are observational – but intervention studies have a special status
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2/8/2011 Intervention studies 8 Analytic study designs Intervention trials (experimental) Cohort studies (observational) Case-control studies (observational) Cross-sectional studies (observational)
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Intervention studies 9 Types of intervention studies Therapeutic trials vs. preventive trials Example of a therapeutic trial: The β - Blocker Heart Attack Trial (B-HAT) The β-Blocker Heart Attack trial. JAMA, Nov. 6, 1981;246(18):2073
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05-InterventionStudies - Principles of Epidemiology for...

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