shiehpow {wmwpow} | R Documentation |
Power Calculation Using the Shieh et. al. Approach
Description
The purpose of shiehpow is to perform a power analysis for a one or two-sided Wilcoxon-Mann-Whitney test using the method developed by Shieh and colleagues.
Arguments
n |
Sample size of first sample (numeric) |
m |
Sample size of second sample (numeric) |
p |
Effect size, P(X<Y) (numeric) |
alpha |
Type I error rate (numeric) |
dist |
The distribution type for the two groups (“exp”, “dexp”, or “norm”) (string) |
sides |
Options are “two.sided” and “one.sided” (string) |
Note
When calculating power for dist=”norm”, shiehpow uses 100,000 draws from a Z ~ N(0,1) distribution for the internal calculation of p2 and p3 from Shieh et al. (2006); thus shiehpow normal distribution power results may vary in the thousandths place from one run to the next.
References
Shieh, G., Jan, S. L., Randles, R. H. (2006). On power and sample size determinations for the Wilcoxon–Mann–Whitney test. Journal of Nonparametric Statistics, 18(1), 33-43.
Mollan K.R., Trumble I.M., Reifeis S.A., Ferrer O., Bay C.P., Baldoni P.L., Hudgens M.G. Exact Power of the Rank-Sum Test for a Continuous Variable, arXiv:1901.04597 [stat.ME], Jan. 2019.
Examples
# We want to calculate the statistical power to compare the distance between mutations on a DNA
# strand in two groups of people. Each group (X and Y) has 10 individuals. We assume that the
# distance between mutations in the first group is exponentially distributed with rate 3. We assume
# that the probability that the distance in the first group is less than the distance in the second
# group (i.e., P(X<Y)) is 0.8. The desired type I error is 0.05.
shiehpow(n = 10, m = 10, p = 0.80, alpha = 0.05, dist = "exp", sides = "two.sided")