| % File src/library/stats/man/power.t.test.Rd |
| % Part of the R package, https://www.R-project.org |
| % Copyright (C) 1995-2014 R Core Team |
| % Distributed under GPL 2 or later |
| |
| \name{power.t.test} |
| \alias{power.t.test} |
| \encoding{UTF-8} |
| \title{Power calculations for one and two sample t tests} |
| \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{ |
| \item{n}{number of observations (per group)} |
| \item{delta}{true difference in means} |
| \item{sd}{standard deviation} |
| \item{sig.level}{significance level (Type I error probability)} |
| \item{power}{power of test (1 minus Type II error probability)} |
| \item{type}{string specifying the type of t test. Can be abbreviated.} |
| \item{alternative}{one- or two-sided test. Can be abbreviated.} |
| \item{strict}{use strict interpretation in two-sided case} |
| \item{tol}{numerical tolerance used in root finding, the default |
| providing (at least) four significant digits.} |
| } |
| \description{ |
| Compute the power of the one- or two- sample t test, |
| or determine parameters to obtain a target power. |
| } |
| |
| \details{ |
| Exactly one of the parameters \code{n}, \code{delta}, \code{power}, |
| \code{sd}, and \code{sig.level} must be passed as \code{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 \code{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 \code{"power.htest"}, a list of the arguments |
| (including the computed one) augmented with \code{method} and |
| \code{note} elements. |
| } |
| |
| \author{Peter Dalgaard. Based on previous work by Claus |
| \enc{Ekstrøm}{Ekstroem}} |
| |
| \note{ |
| \code{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. |
| } |
| \seealso{\code{\link{t.test}}, \code{\link{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") |
| } |
| \keyword{htest} |
| |
| |