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Sample size for a 2-group mean difference confidence interval

Source: R/statpsych1.R
size.ci.mean2.Rd

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. 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.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

References

Bonett DG (2021). Statistical Methods for Psychologists https://dgbonett.sites.ucsc.edu/.

Examples

size.ci.mean2(.01, 81, 12, 1)
#>  n1 n2
#>  32 32

# Should return:
# n1  n2
# 32  32

size.ci.mean2(.05, 4.0, 2.5, 2)
#>  n1 n2
#>  16 32

# Should return:
# n1  n2
# 16  32