Paired observations of blood pressure before and after treatment in 30 patients show non-normally distributed differences. The most appropriate statistical test is:
- A Wilcoxon signed-rank test ✓
- B Paired t-test
- C Mann-Whitney U test
- D McNemar's test
Correct answer: A. Wilcoxon signed-rank test
Explanation
The Wilcoxon signed-rank test is the non-parametric equivalent of the paired t-test, used when paired data do not meet the normality assumption. It ranks the absolute differences and tests whether the median difference is zero. The Mann-Whitney U test (Wilcoxon rank-sum test) is for two independent (unpaired) groups. McNemar's test is for paired nominal/binary categorical data. The paired t-test requires normally distributed differences, which this scenario violates.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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