Pain scores on an ordinal scale were recorded in 30 patients before and after physiotherapy sessions. The differences between paired scores are markedly non-normally distributed. Which test should be used?

• A Wilcoxon signed-rank test ✓
• B Kruskal-Wallis test
• C Student t-test
• D Fisher exact test

Explanation

The Wilcoxon signed-rank test is the non-parametric counterpart of the paired t-test and is designed for paired or matched observations whose differences fail normality, including ordinal scores. Kruskal-Wallis handles three or more independent groups, not paired pairs. Student t-test assumes normally distributed differences, and Fisher exact test applies to categorical data in contingency tables, not to ranked pain scores.

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

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