Computes the sample size in each group (assuming equal sample sizes) required for the Mann-Whitney test with desired power. A planning value of the Mann-Whitney parameter is required. In a 2-group experiment, this parameter is the proportion of members in the population with scores that would be larger under treatment 1 than treatment 2. In a 2-group nonexperiment where participants are sampled from two subpopulations of sizes N1 and N2, the parameter is the proportion of all N1 x N2 pairs in which a member from subpopulation 1 has a larger score than a member from subpopulation 2.

size.test.mann(alpha, pow, p)

Arguments

alpha

alpha level for hypothesis test

pow

desired power

p

planning value of Mann-Whitney parameter

Value

Returns the required sample size per group

References

Noether GE (1987). “Sample size determination for some common nonparametric tests.” Journal of the American Statistical Association, 82(398), 645--647. ISSN 0162-1459, doi:10.1080/01621459.1987.10478478 .

Examples

size.test.mann(.05, .90, .3)
#>      Sample size per group
#> [1,]                    44

# Should return:
#      Sample size per group
# [1,]                    44