Sample size for a 2-group mean ratio confidence interval

Computes the sample size in each group required to estimate a ratio of population means with desired confidence interval precision in a 2-group design. This function requires planning values for each mean and the sample size requirement is very sensitive to these planning values. 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.ratio.mean2(alpha, var, m1, m2, r, R)

Arguments

alpha

alpha level for 1-alpha confidence

var

planning value of average within-group variance

m1

planning value of mean for group 1

m2

planning value of mean for group 2

r

desired upper to lower confidence interval endpoint ratio

R

n2/n1 ratio

Value

Returns the required sample size for each group

Examples

size.ci.ratio.mean2(.05, .4, 3.5, 3.1, 1.2, 1)
#>  n1 n2
#>  70 70

# Should return:
# n1   n2
# 70   70

size.ci.ratio.mean2(.05, .4, 3.5, 3.1, 1.2, 2)
#>  n1  n2
#>  53 106

# Should return:
# n1   n2
# 53  106