size.ci.stdmean2: Sample size for a 2-group standardized mean difference...

In statpsych: Statistical Methods for Psychologists

Sample size for a 2-group standardized mean difference confidence interval

Description

Computes the sample size per group required to estimate two types of population standardized mean differences (unweighted standardizer and single group standardizer) with desired confidence interval precision in a 2-group design. Set the standardized mean difference planning value to the largest value within a plausible range for a conservatively large sample size. Set R = 1 for equal sample sizes. For unequal sample sizes, this function assumes approximately equal population variances.

For more details, see Section 2.13 of Bonett (2021, Volume 1)

Usage

size.ci.stdmean2(alpha, d, w, R)

Arguments

alpha	alpha level for 1-alpha confidence
d	planning value of standardized mean difference
w	desired confidence interval width
R	n2/n1 ratio

Value

Returns the required sample size per group for each standardizer

References

\insertRef

Bonett2009statpsych

\insertRef

Bonett2021statpsych

Examples

size.ci.stdmean2(.05, 1.0, .5, 1)

# Should return:
#                              n1  n2
# Unweighted standardizer:    139 139
# Single group standardizer:  154 154

size.ci.stdmean2(.05, 1.0, .5, 2)

# Should return:
#                              n1  n2
# Unweighted standardizer:    104 208
# Single group standardizer:  116 232
 

statpsych documentation built on Jan. 13, 2026, 1:07 a.m.