size.ci.mean2: Sample size for a 2-group mean difference confidence interval

In statpsych: Statistical Methods for Psychologists

Sample size for a 2-group mean difference confidence interval

Description

Computes the sample size for each group required to estimate a population mean difference with desired confidence interval precision 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.

Usage

size.ci.mean2(alpha, var, w, R)

Arguments

alpha	alpha level for 1-alpha confidence
var	planning value of average within-group variance
w	desired confidence interval width
R	n2/n1 ratio

Value

Returns the required sample size for each group

Examples

size.ci.mean2(.05, 37.1, 5, 1)

# Should return:
# n1  n2
# 47  47

size.ci.mean2(.05, 37.1, 5, 3)

# Should return:
# n1  n2
# 32  96

size.ci.mean2(.05, 37.1, 5, .5)

# Should return:
# n1  n2
# 70  35
 

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