stats (version 3.3)

power.prop.test: Power Calculations for Two-Sample Test for Proportions

Description

Compute the power of the two-sample test for proportions, or determine parameters to obtain a target power.

Usage

power.prop.test(n = NULL, p1 = NULL, p2 = NULL, sig.level = 0.05,
                power = NULL,
                alternative = c("two.sided", "one.sided"),
                strict = FALSE, tol = .Machine$double.eps^0.25)

Arguments

n
number of observations (per group)
p1
probability in one group
p2
probability in other group
sig.level
significance level (Type I error probability)
power
power of test (1 minus Type II error probability)
alternative
one- or two-sided test. Can be abbreviated.
strict
use strict interpretation in two-sided case
tol
numerical tolerance used in root finding, the default providing (at least) four significant digits.

Value

  • Object of class "power.htest", a list of the arguments (including the computed one) augmented with method and note elements.

encoding

UTF-8

Details

Exactly one of the parameters n, p1, p2, power, and sig.level must be passed as NULL, and that parameter is determined from the others. Notice that sig.level has a non-NULL default so NULL must be explicitly passed if you want it computed.

If strict = TRUE is used, the power will include the probability of rejection in the opposite direction of the true effect, in the two-sided case. Without this the power will be half the significance level if the true difference is zero.

See Also

prop.test, uniroot

Examples

Run this code
power.prop.test(n = 50, p1 = .50, p2 = .75)      ## => power = 0.740
power.prop.test(p1 = .50, p2 = .75, power = .90) ## =>     n = 76.7
power.prop.test(n = 50, p1 = .5, power = .90)    ## =>    p2 = 0.8026
power.prop.test(n = 50, p1 = .5, p2 = 0.9, power = .90, sig.level=NULL)
                                                 ## => sig.l = 0.00131
power.prop.test(p1 = .5, p2 = 0.501, sig.level=.001, power=0.90)
                                                 ## => n = 10451937

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