| size.ci.stdmean2 {statpsych} | R Documentation |
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.
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
Bonett DG (2009). “Estimating standardized linear contrasts of means with desired precision.” Psychological Methods, 14(1), 1–5. ISSN 1939-1463, doi:10.1037/a0014270.
Examples
size.ci.stdmean2(.05, .75, .5, 1)
# Should return:
# n1 n2
# Unweighted standardizer: 132 132
# Single group standardizer: 141 141