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Chapter 18 Part B: Case-Control Studies and Test for Trend

Chapter 18 Part B: Case-Control Studies and Test for Trend. Chapter 18, Part B = Case-Control. Case-Control (type III) sample All population cases Select 1 or more non-cases (“controls”) per case Ascertain exposure status of cases and controls Cross-tabulate results.

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Chapter 18 Part B: Case-Control Studies and Test for Trend

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  1. Chapter 18Part B: Case-Control Studiesand Test for Trend

  2. Chapter 18, Part B = Case-Control • Case-Control (type III) sample • All population cases • Select 1 or more non-cases (“controls”) per case • Ascertain exposure status of cases and controls • Cross-tabulate results

  3. Case-Control vs. Cohort • Case-control studies select cases and non-cases and then ascertain exposure status • Cohort studies select exposed and non-exposed individuals and then ascertain occurrence over time http://en.wikipedia.org/wiki/Case-control_study

  4. Control Selection “Density Sampling” Potential controls, time t1 Potential controls time t1 Potential controls, time t2

  5. Cross-tabulate Odds Ratio cross-product ratio Interpretation: OR stochastically = RR

  6. Breslow Day Data Set 1 • Disease: esophageal cancer • Exposure: alcohol consumption dichotomized at 80 gms/day • Cross-tabulate exposure and disease b1 a1 a2 b2 Exposed individuals at about 5 times the risk as non-exposed individuals

  7. (1– α)100% CI for the OR

  8. 90% CI for OR – Example Likely location of OR after accounting for random error

  9. WinPEPI > Compare2 > A. Data entry Output 90% CI for OR = (4.22, 7.52)

  10. Ordinal Exposure Compare each exposure level to least exposed level

  11. Dose-response Ordinal Exposure

  12. Mantel Test for Trend • H0: no trend in population risks • Test statistic: Mantel chi-square for trend, or zstat equivalent • P value  • Assess evidence against H0 Nathan Mantel (1919 – 2002) Public domain photo

  13. Mantel Test for Trend • H0: no trend in population risks • Test stat.: WinPEPI > Compare2 > F2. Ordinal • P value  • Conclusion: strong evidence of a trend

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