1. Chapter 18 Part C: Matched Pairs
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Chapter 18 Part C: Matched Pairs
7/30/2019
Basic Biostat

2. §18.6 Matched Pairs Binary data
Match on extraneous factors that can confound results
1:1 match
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3. Case-Control Example Case-control study on colon polyp re-occurrence
Cases & controls matched on age, clinic, sex and other potentially confounding factors
Let “exposure” = low fruit/veg consumption
Ascertain exposure in case-control pairs
45 pairs: case exposed and control not exposed
24 pairs: control was exposed and case not exposed
Case exposed
Case non-exposed
Control exposed ? 24
Control non-exposed 45
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4. Matched-Pairs Odds Ratio
Case E+
Case E−
Control E+ a b
Control E− c d
Interpret like any other odds ratio i.e, as a relative risk
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5. Colon polyp recurrence / low fruit illustrative data
Case E+
Case E−
Cntl E+ ? 24
Cntl E− 45
88% higher risk w/ low fruit/veg consumption
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6. Confidence Interval for OR
Matched Pairs
Case E+
Case E−
Control E+ a b
Control E− c d
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7. 95% CI for OR Colon polyps illustrative example
Interpret like any other CI
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8. WinPEPI > PairEtc > A.
Input
WinPEPI produces these superior confidence limits
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9. Cohort Matched-Pairs Exposed and non-exposed matched pairs
Smoking and non-smoking twins (exposure = smoking)
Disease = earlier death
17 twin-pairs in which smoking twin died first
5 twin-pairs in which non-smoking twin died first
Smoker D+
Smoker D−
Non-smoker D+ 5
Non-smoker D− 17
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10. Hypothesis Test A. H0: OR = 1 (“no association”)
B. McNemar’s z (or equivalent chi-square)
C. P-value
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11. Twins Mortality Example
Conclude: Good evidence against H0
(or other reasonable P-value interpretation)
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