In a follow-up study, 100 smokers are assessed at baseline and again after counselling. Each subject is classified as smoker or non-smoker on both occasions. To test whether the quit rate changed significantly after counselling, the appropriate test is:
- A McNemar test ✓
- B Fisher exact test
- C Standard chi-square test
- D Wilcoxon rank sum test
Correct answer: A. McNemar test
Explanation
The data consist of paired binary observations on the same individuals measured twice, which is precisely the indication for McNemar test. It uses only the discordant pairs, those who changed status, ignoring concordant pairs who stayed the same. C standard chi-square treats the two time points as independent groups, which is wrong here. Wilcoxon rank sum compares two independent groups of continuous or ordinal data.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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