WMWssp_noether {WMWssp}

Sample size calculation for the Wilcoxon-Mann-Whitney test using the Noether formula

Description

This function calculates the sample size for given type-I and type-II error probabilities using Noether's formula. If ties are present then prior information is needen.

Usage

WMWssp_noether(alpha, power, t, p, x = c(0), ties = FALSE)

Arguments

alpha

two sided type I error rate

power

power: detect a relative effect p at least with the specified power

t

proportion of subjects in the first group (between 0 and 1)

p

relative effect

x

prior information is only needed in case of ties

ties

TRUE if ties are possible (non continuous distribution), otherwise FALSE

Value

Returns an object from class WMWssp containing

result

A dataframe with the results.

t

The allocation rate which was used.

alpha

The type-I error rate which was used.

power

The power which was used.

N

The sample size needed.

References

Noether, G. E. (1987). Sample Size Determination for Some Common Nonparametric Tests. Journal of the American Statistical Association 85, 645.647.

Examples

# Prior information for the reference group
x <- c(315,375,356,374,412,418,445,403,431,410,391,475,379)
# generate data for treatment group based on a shift effect
y <- x - 20
# this data leads to a relative effect of p = 0.349

# calculate sampe size for a balanced design
ssp <- WMWssp_noether(alpha = 0.05, power = 0.8, t =1/2, p = 0.349)
summary(ssp)