size.test.prop2: Sample size for a test of a 2-group proportion difference

In statpsych: Statistical Methods for Psychologists

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

Description

Computes the sample size in each group required to test a difference in population proportions with desired power (using a continuity correction) in a 2-group design. This function requires planning values for both proportions. Set each proportion planning value to .5 for a conservatively large sample size requirement. This function does not require the planning value for the proportion difference (effect size) to equal the difference of the two proportion planning values; for example, the planning value of the proportion difference could be set equal to a minimally interesting effect size.

Usage

size.test.prop2(alpha, pow, p1, p2, es)

Arguments

alpha	alpha level for hypothesis test
pow	desired power
p1	planning value of proportion for group 1
p2	planning value of proportion for group 2
es	planning value of proportion difference (effect size)

Value

Returns the required sample size for each group

Examples

size.test.prop2(.05, .8, .5, .5, .2)

# Should return:
# Sample size per group
#                   109

size.test.prop2(.05, .8, .3, .1, .2)
# Should return:
# Sample size per group
#                    71

statpsych documentation built on June 10, 2025, 5:11 p.m.