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Sample size for a 2-group proportion difference confidence interval

Source: R/statpsych3.R
size.ci.prop2.Rd

Computes the sample size in each group required to estimate a difference of proportions with desired confidence interval precision in a 2-group design. Set the proportion planning values to .5 for a conservatively large sample size. Set R = 1 for equal sample sizes.

Usage

size.ci.prop2(alpha, p1, p2, w, R)

Arguments

alpha

alpha level for 1-alpha confidence

p1

planning value of proportion for group 1

p2

planning value of proportion for group 2

w

desired confidence interval width

R

n2/n1 ratio

Value

Returns the required sample size for each group

Examples

size.ci.prop2(.05, .4, .2, .15, 1)
#>   n1  n2
#>  274 274

# Should return:
#   n1  n2
#  274 274

size.ci.prop2(.05, .4, .2, .15, .5)
#>   n1  n2
#>  383 192

# Should return:
#   n1  n2
#  383 192