size.equiv.mean2 {statpsych}

Sample size for a 2-group mean equivalence test

Description

Computes the sample size in each group (assuming equal sample sizes) required to perform an equivalence test for the difference in population means with desired power in a 2-group design. The value of h specifies a range of practical equivalence, -h to h, for the difference in population means. The planning value for the absolute mean difference must be less than h. Equivalence tests often require a very large sample size. Equivalence tests usually use 2 x alpha rather than alpha (e.g., use alpha = .10 rather alpha = .05). Set the variance planning value to the largest value within a plausible range for a conservatively large sample size.

Usage

size.equiv.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 limit for range of practical equivalence

Value

Returns the required sample size for each group

Examples

size.equiv.mean2(.10, .80, 15, 2, 4)

# Should return:
# Sample size per group 
#                    50