# power.t.test

##### Power calculations for one and two sample t tests

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

- Keywords
- htest

##### 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.

##### See Also

##### Examples

`library(stats)`

```
# 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")
# }
```

*Documentation reproduced from package stats, version 3.5.0, License: Part of R 3.5.0*