Wilcoxon Rank-sum Test
A non-parametric test for independent samples testing whether two populations have the same distribution, using ranks from all observations combined.
Real World
Ofsted researchers compare GCSE maths scores from 30 comprehensive schools against 25 grammar schools using a Wilcoxon rank-sum test, ranking all 55 scores together to see whether one school type consistently outperforms the other.
Exam Focus
Clearly state samples are independent and unpaired — confusing this with the signed-rank test for paired data is a common lost-mark error.
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