Computes the sample size in each group required to test a difference in
population means with desired power 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. For
unequal sample sizes, this function assumes approximately equal population
variances.
For more details, see Section 2.14 of Bonett (2021, Volume 1)
Usage
size.test.mean2(alpha, pow, var, es, R)
Arguments
- alpha
alpha level for hypothesis test
- pow
desired power
- var
planning value of average within-group variance
- es
planning value of mean difference
- R
n2/n1 ratio
Value
Returns the required sample size for each group
References
Bonett DG (2021).
Statistical Methods for Psychologists https://dgbonett.sites.ucsc.edu/.
Examples
size.test.mean2(.05, .95, 100, 10, 1)
#> n1 n2
#> 27 27
# Should return:
# n1 n2
# 27 27
size.test.mean2(.05, .95, 100, 10, 3)
#> n1 n2
#> 19 57
# Should return:
# n1 n2
# 19 57
size.test.mean2(.05, .95, 100, 10, .5)
#> n1 n2
#> 40 20
# Should return:
# n1 n2
# 40 20