Transcription of Statistics: 2.3 The Mann-Whitney U Test - statstutor
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Statistics: 2.3 The Mann-Whitney U Test - statstutor
Statistics: The Mann-Whitney U TestRosie Shier. IntroductionThe Mann-Whitney U test is a non-parametric test that can be used in place of anunpaired t-test. It is used to test the null hypothesis that two samples come from thesame population ( have the same median) or, alternatively, whether observations in onesample tend to be larger than observations in the other. Although it is a non-parametrictest it does assume that the two distributions are similar in Carrying out the Mann-Whitney U testSuppose we have a sample ofnxobservations{x1, x2, .. xn}in one group ( from onepopulation) and a sample ofnyobservations{y1, y2.}
7. If we use a normal approximation we get: z = U − nxny r 2 n xn y(N +1) 12 = q3−10 50/3 = −1.715 This gives a two-sided p-value of p = 0.09. The exact test and the normal approximation give similar results. We would conclude that there is no real evidence that the age at diagnosis is different for males and females,
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