Pain scores are measured in the same patients before and after physiotherapy. The differences between paired measurements are severely non-normally distributed. The appropriate test for significance is:

• A Paired t-test
• B Wilcoxon signed rank test ✓
• C Mann-Whitney U test
• D Kruskal-Wallis test

Explanation

For paired observations whose differences violate normality, the Wilcoxon signed rank test is the standard non-parametric analogue of the paired t-test. Mann-Whitney U and Kruskal-Wallis apply to independent samples, not paired data, so they fail on design grounds even though they are non-parametric. The paired t-test requires approximately normally distributed differences, which the stem explicitly excludes.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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