In an individually matched case-control study of sudden cardiac death and recent cocaine use, there are 30 pairs in which the case used cocaine and the control did not, and 10 pairs in which the control used cocaine and the case did not. The matched-pairs odds ratio is:
- A 0.33
- B 3.0 ✓
- C 4.0
- D 9.0
Correct answer: B. 3.0
Explanation
For pair-matched data the odds ratio uses only the discordant pairs: b divided by c, where b is the number of pairs with an exposed case and unexposed control and c the reverse. Here 30 divided by 10 gives 3.0. Concordant pairs, where both members share the same exposure status, contribute nothing to the estimate. Option C would result from incorrectly including concordant pairs, and option A simply inverts the correct ratio.
Reference: Gordis Epidemiology, 6th ed.
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