Mann-Whitney test | Mann-Whitney U test sample size
HowitworksTheMann-Whitneytest,alsocalledtheWilcoxonranksumtest,isanonparametrictestthatcomparestwounpairedgroups.ToperformtheMann-Whitneytest,Prismfirstranksallthevaluesfromlowtohigh,payingnoattentiontowhichgroupeachvaluebelongs.Thesmallestnumbergetsarankof1.Thelargestnumbergetsarankofn,wherenisthetotalnumberofvaluesinthetwogroups.Prismthenaveragestheranksineachgroup,andreportsthetwoaverages.Ifthemeansoftheranksinthetwogroupsareverydifferent,thePvaluewillbesmall.PvalueYoucantinterpretaPvalue...
How it worksThe Mann-Whitney test, also called the Wilcoxon rank sum test, is a nonparametric test that compares two unpaired groups. To perform the Mann-Whitney test, Prism first ranks all the values from low to high, paying no attention to which group each value belongs. The smallest number gets a rank of 1. The largest number gets a rank of n, where n is the total number of values in the two groups. Prism then averages the ranks in each group, and reports the two averages. If the means of the ranks in the two groups are very different, the P value will be small.
P valueYou cant interpret a P value until you know the null hypothesis being tested. For the Mann-Whitney test, the null hypothesis is a bit hard to understand. The null hypothesis is that the distributions of both groups are identical, so that there is a 50% probability that an observation from a value randomly selected from one population exceeds an observation randomly ...