Sample size for a confidence interval for the difference of any type of parameter

Computes the sample size required to estimate a difference in population parameters with desired precision in a 2-group design using a standard error for a parameter estimate from a prior or pilot study. This function can be used with any type of parameter where the standard error of the parameter estimate is a function of the square root of the sample size (most parameter estimates have this property). This function also assumes that the sampling distribution of the parameter estimate is approximately normal in large samples. Set R = 1 for equal sample sizes.

Usage

size.ci.gen2(alpha, se, n0, w, R)

Arguments

alpha: alpha level for hypothesis test
se: standard error of parameter estimate from prior/pilot study
n0: sample size of prior/pilot study
w: desired confidence interval width
R: n2/n1 ratio

Value

Returns the required sample size for each group

Examples

size.ci.gen2(.05, .175, 30, .8, 1)
#>  n1 n2
#>  45 45

# Should return:
# n1  n2
# 45  45