# power.prop.test

0th

Percentile

##### Power Calculations for Two-Sample Test for Proportions

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

Keywords
htest
##### 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.
##### 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.

##### Value

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

##### Note

uniroot is used to solve power equation for unknowns, so you may see errors from it, notably about inability to bracket the root when invalid arguments are given. If one of them is computed p1 < p2 will hold, although this is not enforced when both are specified.

##### encoding

UTF-8

prop.test, uniroot
library(stats) 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