size.ci.prop2: Sample size for a 2-group proportion difference confidence...

In statpsych: Statistical Methods for Psychologists

Sample size for a 2-group proportion difference confidence interval

Description

Computes the sample size in each group 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. Set R = 1 for equal sample sizes.

Usage

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

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
R	n2/n1 ratio

Value

Returns the required sample size for each group

Examples

size.ci.prop2(.05, .4, .2, .15, 1)

# Should return:
#   n1  n2
#  274 274

size.ci.prop2(.05, .4, .2, .15, .5)

# Should return:
#   n1  n2
#  383 192

statpsych documentation built on April 4, 2025, 3:20 a.m.