1. Chapter 18 Part B: Case-Control Studies and Test for Trend
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Chapter 18 Part B: Case-Control Studies and Test for Trend
11/14/2018
Basic Biostat

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
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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
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4. Control Selection “Density Sampling” Potential controls, time t1
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5. Cross-tabulate  Odds Ratio
Cases
Controls E+ a1 b1 E− a2 b2 m1 m2
cross-product ratio
Interpretation: OR stochastically = RR
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6. Breslow Day Data Set 1 Disease: esophageal cancer
Exposure: alcohol consumption dichotomized at 80 gms/day
Cross-tabulate exposure and disease a1 b1 a2 b2
Exposed individuals at about 5 times the risk as non-exposed individuals
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7. (1– α)100% CI for the OR
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8. Likely location of OR after accounting for random error
90% CI for OR – Example D+ D− E+ 96
109 E−
104
666
Likely location of OR after accounting for random error
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9. WinPEPI > Compare2 > A.
Data entry
Output
90% CI for OR = (4.22, 7.52)
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10. Compare each exposure level to least exposed level
Ordinal Exposure
Compare each exposure level to least exposed level
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11. Ordinal Exposure
Dose-response
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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
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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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