power.t.test: Power calculations for one and two sample t tests

Description

Compute power of test, or determine parameters to obtain target power.

Usage

power.t.test(n = NULL, delta = NULL, sd = 1, sig.level = 0.05, power = NULL, type = c("two.sample", "one.sample", "paired"), alternative = c("two.sided", "one.sided"), strict = FALSE)

Arguments

Number of observations (per group)

delta

True difference in means

Standard deviation

sig.level

Significance level (Type I error probability)

power

Power of test (1 minus Type II error probability)

type

Type of t test

alternative

One- or two-sided test

strict

Use strict interpretation in two-sided case

Value

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

Details

Exactly one of the parameters n, delta, power, sd, and sig.level must be passed as NULL, and that parameter is determined from the others. Notice that the last two have non-NULL defaults so NULL must be explicitly passed if you want to compute them.

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.

Examples

Run this code

 power.t.test(n = 20, delta = 1)
 power.t.test(power = .90, delta = 1)
 power.t.test(power = .90, delta = 1, alternative = "one.sided")