ranksum: Power calculation for rank-sum test

In powertools: Power and Sample Size Tools

Power calculation for rank-sum test

Description

This function performs power and sample size calculations for the Wilcoxon-Mann-Whitney rank-sum test, also called the Mann-Whitney U test, which is the nonparametric analog of the two independent sample t test. Calculations are based on the approximation given by Noether (1987) Sample size determination for some common nonparametric tests. JASA 82(398):645-647.

Usage

ranksum(
  n1 = NULL,
  n.ratio = 1,
  p = NULL,
  alpha = 0.05,
  power = NULL,
  sides = 2,
  v = FALSE
)

Arguments

n1	The sample size in group 1.
n.ratio	The ratio n2/n1 between the sample sizes of two groups; defaults to 1 (equal group sizes).
p	The probability that an observation in group 2 is greater than an observation in group 1 (P(Y>X).
alpha	The significance level (type 1 error rate); defaults to 0.05.
power	The specified level of power.
sides	Either 1 or 2 (default) to specify a one- or two-sided hypothesis test.
v	Either TRUE for verbose output or FALSE (default) to output computed argument only.

Details

Due to symmetry, the power for p is equal to the power for 1 - p. Therefore, when solving for p, two values, p and 1 - p, are returned.

Value

A list of the arguments (including the computed one).

Examples

ranksum(n1 = 10, n.ratio = 1, p = 0.8, alpha = 0.05, power = NULL, sides = 2)

powertools documentation built on April 4, 2025, 5:02 a.m.