Pain scores measured on a visual analogue scale are recorded before and after physiotherapy in the same 30 patients. The score differences are markedly skewed. Which test is most appropriate?
- A Paired t-test
- B Wilcoxon signed-rank test ✓
- C Mann-Whitney U test
- D Kruskal-Wallis test
Correct answer: B. Wilcoxon signed-rank test
Explanation
Wilcoxon signed-rank test is the non-parametric counterpart of the paired t-test and ranks the absolute within-patient differences, so it needs no normality assumption and handles skewed or ordinal paired data. Mann-Whitney U test compares two independent groups, and Kruskal-Wallis compares three or more independent groups, so neither matches the paired design. The paired t-test would be inappropriate given the skewed differences in this small sample.
Reference: Mahajan's Methods in Biostatistics for Medical Students and Research Workers, 9th ed.
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