A researcher wishes to compare mean birth weights across three dietary groups using parametric analysis. After applying the Shapiro-Wilk test, the data in one group shows significant non-normality (p = 0.02). Which is the MOST appropriate non-parametric alternative to one-way ANOVA?
- A Mann-Whitney U test
- B Wilcoxon signed-rank test
- C Kruskal-Wallis test ✓
- D Friedman test
Correct answer: C. Kruskal-Wallis test
Explanation
The Kruskal-Wallis test is the non-parametric equivalent of one-way ANOVA and is used to compare medians across three or more independent groups when normality assumptions are violated. Mann-Whitney U compares two independent groups; Wilcoxon signed-rank compares two related samples; Friedman test is used for three or more related (repeated-measures) groups — none of these are appropriate substitutes for one-way ANOVA across three independent groups.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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