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Three Main Types of Non-Experimental Studies

Three Main Types of Non-Experimental Studies. Cross-sectional : compare prevalences or cross-sectional rates in sub-groups (no follow-up of individuals) Cohort : recruit cohort  sub-divide cohort  individual follow-up over time  compare incidences in sub-groups

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Three Main Types of Non-Experimental Studies

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  1. Three Main Types of Non-Experimental Studies • Cross-sectional: compare prevalences or cross-sectional rates in sub-groups (no follow-up of individuals) • Cohort: recruit cohort  sub-divide cohort  individual follow-up over time  compare incidences in sub-groups • Case-control: identify cases and a small number of non-cases  compare exposure experience of cases and non-cases Intro to Case-Control Studies

  2. For the sake of comparison, let’s first consider cohort designs… • Recruit cohort • Classify individual as exposed or non-exposed • Follow exposed and non-exposed sub-cohorts over time to determine incidence exposed sub-cohort → Incidenceexposed Closed population Compare Incidences non-exposed sub-cohort → Incidencenon-exposed Intro to Case-Control Studies

  3. …in contrast, case-control studies • Identifying cases • Identify a small sample of non-cases (“controls”) • Determine exposure histories of cases and controls All cases Population Very efficient for studying rare diseases Small number of non-cases But can NOT estimate incidence Intro to Case-Control Studies

  4. Case-Control Case-control studies cannot estimate incidence, BUT can estimate relative incidence (i.e., relative risk) via the odds ratio (cross-product ratio): Intro to Case-Control Studies

  5. Toxic Shock Syndrome and Tampon Use, Wisconsin, 1980 30 71 1 22 Intro to Case-Control Studies

  6. Interpretation of the Odds Ratio • When the disease is rare, OR = RR (slightly more complicated than this, but nevermind) • The illustrative OR of 9.3 suggests that tampon users had 9.3 times the risk as non-tampon users • [The suspected brand of tampon has since been removed from the market] Intro to Case-Control Studies

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