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:

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. Shiny interface by Chris Miller

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”)

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