Compute sample size to test the hypothesis that two samples come from the same population against that Y's tend to be larger than X's.
1 2  sampleSizeWilcoxTwoSample(a = 0.05, b = 0.2, c = 0.5,
pxy = 0.75, two.sided = TRUE)

a 
Significance level of test. 
b 
Desired power of test. 
c 
Proportion of observations in group 1: c = m / (m + n) (c = 0.5 means equally sized groups). 
pxy 
A value for the probability P(Y > X). 
two.sided 
If 
Given two independent samples X_1, ..., X_m and Y_1, ..., Y_n, we want to test the hypothesis that the two samples come from the same population against that Y's tend to be larger than X's.
m 
Sample size of the first group. 
n 
Sample size of the second group. 
Kaspar Rufibach
kaspar.rufibach@gmail.com
Nother, G.E. (1987). Sample Size Determination for Some Common Nonparametric Tests JASA, 82, 644–647.
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