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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.

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)
#>  n1 n2
#>  47 47

# Should return:
# n1  n2
# 47  47

size.ci.mean2(.05, 37.1, 5, 3)
#>  n1 n2
#>  32 96

# Should return:
# n1  n2
# 32  96

size.ci.mean2(.05, 37.1, 5, .5)
#>  n1 n2
#>  70 35

# Should return:
# n1  n2
# 70  35