size.test.prop2 {statpsych}

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 and a continuity correction in a 2-group design. This function requires planning values for both proportions. Set each proportion planning value to .5, or a value closest to .5 within a plausible range, for a conservatively large sample size requirement. This function does not use the typical sample size approach where the effect size is assumed to equal the difference in proportion planning values. 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