What hypotheses do -nonparametric- two-group tests actually test 

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In this article, I discuss measures of effect size for two-group comparisons where data are not appropriately analyzed by least-squares methods. The Mann–Whitney test calculates a statistic that is a very useful measure of effect size, particularly suited to situations in which differences are measured on scales that either are ordinal or use arbitrary scale units. Both the difference in medians and the median difference between groups are also useful measures of effect size.
Keywords: ranksum ; Wilcoxon rank-sum test ; Mann–Whitney statistic ; Hodges–Lehman median shift ; effect size ; qreg
Subject(s): Research Methods/ Statistical Methods
Issue Date: 2012
Publication Type: Journal Article
DOI and Other Identifiers: st0253 (Other)
PURL Identifier: http://purl.umn.edu/207998 Published in: Stata Journal, Volume 12, Number 2 Page range: 182-190
Total Pages: 11
Record appears in: Stata Journal
Autor: Conroy, Ronán M.
Fuente: http://ageconsearch.umn.edu/record/207998?ln=en