R: Power calculations for one and two sample t tests

power.t.test {stats} | R Documentation

## Power calculations for one and two sample t tests

### Description

Compute the power of the one- or two- sample t test, or determine parameters to obtain a 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, tol = .Machine$double.eps^0.25)

### Arguments

`n` | number of observations (per group)
`delta` | true difference in means
`sd` | standard deviation
`sig.level` | significance level (Type I error probability)
`power` | power of test (1 minus Type II error probability)
`type` | string specifying the type of t test. Can be abbreviated.
`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`, `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.

### 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 the power equation for unknowns, so you may see errors from it, notably about inability to bracket the root when invalid arguments are given.

### Author(s)

Peter Dalgaard. Based on previous work by Claus Ekstrøm

### See Also

`t.test`, `uniroot`

### Examples

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

[Package stats version 3.5.1 Index]