size.test.mean2: Sample size for a test of a 2-group mean difference

In statpsych: Statistical Methods for Psychologists

Sample size for a test of a 2-group mean difference

Description

Computes the sample size in each group required to test a difference in population means with desired power in a 2-group design. Set the variance planning value to the largest value within a plausible range for a conservatively large sample size. Set R = 1 for equal sample sizes. For unequal sample sizes, this function assumes approximately equal population variances.

For more details, see Section 2.14 of Bonett (2021, Volume 1)

Usage

size.test.mean2(alpha, pow, var, es, R)

Arguments

alpha	alpha level for hypothesis test
pow	desired power
var	planning value of average within-group variance
es	planning value of mean difference
R	n2/n1 ratio

Value

Returns the required sample size for each group

References

\insertRef

Bonett2021statpsych

Examples

size.test.mean2(.05, .95, 100, 10, 1) 

# Should return:
# n1  n2
# 27  27

size.test.mean2(.05, .95, 100, 10, 3) 

# Should return:
# n1  n2
# 19  57

size.test.mean2(.05, .95, 100, 10, .5) 

# Should return:
# n1  n2
# 40  20
 

statpsych documentation built on Jan. 13, 2026, 1:07 a.m.