stats (version 3.6.2)

# power.t.test: 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.

## 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.

`t.test`, `uniroot`

## Examples

Run this code
``````# NOT RUN {
power.t.test(n = 20, delta = 1)
power.t.test(power = .90, delta = 1)
power.t.test(power = .90, delta = 1, alternative = "one.sided")
# }
``````

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