size.supinf.mean2 {statpsych}

Sample size for a 2-group mean superiority or noninferiority test

Description

Computes the sample size in each group (assuming equal sample sizes) required to perform a superiority or noninferiority test for the difference in population means with desired power in a 2-group design. For a superiority test, specify the upper limit (h) for the range of practical equivalence and specify an effect size (es) such that es > h. For a noninferiority test, specify the lower limit (-h) for the range of practical equivalence and specify an effect size such that es > -h. Set the variance planning value to the largest value within a plausible range for a conservatively large sample size.

Usage

size.supinf.mean2(alpha, pow, var, es, h)

Arguments

alpha

alpha level for hypothesis test

pow

desired power

var

planning value of average within-group variance

es

planning value of mean difference

h

upper or lower limit for range of practical equivalence

Value

Returns the required sample size for each group

Examples

size.supinf.mean2(.05, .80, 225, 9, 4)

# Should return:
# Sample size per group 
#                   143