size.ci.prop2 {statpsych}

Sample size for a 2-group proportion difference confidence interval

Description

Computes the sample size in each group (assuming equal sample sizes) required to estimate a difference of proportions with desired confidence interval precision in a 2-group design. Set the proportion planning values to .5 for a conservatively large sample size.

Usage

size.ci.prop2(alpha, p1, p2, w)

Arguments

alpha

alpha level for 1-alpha confidence

p1

planning value of proportion for group 1

p2

planning value of proportion for group 2

w

desired confidence interval width

Value

Returns the required sample size for each group

Examples

size.ci.prop2(.05, .4, .2, .15)

# Should return:
# Sample size per group
#                   274