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 twosided test. Can be abbreviated.
 strict
 use strict interpretation in twosided 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
nonNULL 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 twosided
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)
power.t.test(n = 20, delta = 1)
power.t.test(power = .90, delta = 1)
power.t.test(power = .90, delta = 1, alternative = "one.sided")