Mann–Whitney U test when variances are unequal

@article{Kasuya2001MannWhitneyUT,
  title={Mann–Whitney U test when variances are unequal},
  author={Eiiti Kasuya},
  journal={Animal Behaviour},
  year={2001},
  volume={61},
  pages={1247-1249}
}
  • E. Kasuya
  • Published 1 June 2001
  • Mathematics
  • Animal Behaviour
The Mann–Whitney U test is one of the most widely used statistical tests in studies of behaviour. In 1999, 42 of 151 articles surveyed (27.8%) in volume 56 of Animal Behaviour used this test, and another eight used its extension to more than two samples: the Kruskal–Wallis test. The Mann–Whitney U test, like many other nonparametric tests based on rank, assumes equal variances in the two populations (in this commentary, I use the term population only in the statistical sense) from which the two… 

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