| % File src/library/stats/man/bartlett.test.Rd |
| % Part of the R package, https://www.R-project.org |
| % Copyright 1995-2018 R Core Team |
| % Distributed under GPL 2 or later |
| |
| \name{bartlett.test} |
| \alias{bartlett.test} |
| \alias{bartlett.test.default} |
| \alias{bartlett.test.formula} |
| \title{Bartlett Test of Homogeneity of Variances} |
| \description{ |
| Performs Bartlett's test of the null that the variances in each of the |
| groups (samples) are the same. |
| } |
| \usage{ |
| bartlett.test(x, \dots) |
| |
| \method{bartlett.test}{default}(x, g, \dots) |
| |
| \method{bartlett.test}{formula}(formula, data, subset, na.action, \dots) |
| } |
| \arguments{ |
| \item{x}{a numeric vector of data values, or a list of numeric data |
| vectors representing the respective samples, or fitted linear model |
| objects (inheriting from class \code{"lm"}).} |
| \item{g}{a vector or factor object giving the group for the |
| corresponding elements of \code{x}. |
| Ignored if \code{x} is a list.} |
| \item{formula}{a formula of the form \code{lhs ~ rhs} where \code{lhs} |
| gives the data values and \code{rhs} the corresponding groups.} |
| \item{data}{an optional matrix or data frame (or similar: see |
| \code{\link{model.frame}}) containing the variables in the |
| formula \code{formula}. By default the variables are taken from |
| \code{environment(formula)}.} |
| \item{subset}{an optional vector specifying a subset of observations |
| to be used.} |
| \item{na.action}{a function which indicates what should happen when |
| the data contain \code{NA}s. Defaults to |
| \code{getOption("na.action")}.} |
| \item{\dots}{further arguments to be passed to or from methods.} |
| } |
| \details{ |
| If \code{x} is a list, its elements are taken as the samples or fitted |
| linear models to be compared for homogeneity of variances. In this |
| case, the elements must either all be numeric data vectors or fitted |
| linear model objects, \code{g} is ignored, and one can simply use |
| \code{bartlett.test(x)} to perform the test. If the samples are not |
| yet contained in a list, use \code{bartlett.test(list(x, ...))}. |
| |
| Otherwise, \code{x} must be a numeric data vector, and \code{g} must |
| be a vector or factor object of the same length as \code{x} giving the |
| group for the corresponding elements of \code{x}. |
| } |
| \value{ |
| A list of class \code{"htest"} containing the following components: |
| \item{statistic}{Bartlett's K-squared test statistic.} |
| \item{parameter}{the degrees of freedom of the approximate chi-squared |
| distribution of the test statistic.} |
| \item{p.value}{the p-value of the test.} |
| \item{method}{the character string |
| \code{"Bartlett test of homogeneity of variances"}.} |
| \item{data.name}{a character string giving the names of the data.} |
| } |
| \seealso{ |
| \code{\link{var.test}} for the special case of comparing variances in |
| two samples from normal distributions; |
| \code{\link{fligner.test}} for a rank-based (nonparametric) |
| \eqn{k}-sample test for homogeneity of variances; |
| \code{\link{ansari.test}} and \code{\link{mood.test}} for two rank |
| based two-sample tests for difference in scale. |
| } |
| \references{ |
| Bartlett, M. S. (1937). |
| Properties of sufficiency and statistical tests. |
| \emph{Proceedings of the Royal Society of London Series A} |
| \bold{160}, 268--282. |
| \doi{10.1098/rspa.1937.0109}. |
| } |
| |
| % FIXME: could use something more interesting here |
| \examples{ |
| require(graphics) |
| |
| plot(count ~ spray, data = InsectSprays) |
| bartlett.test(InsectSprays$count, InsectSprays$spray) |
| bartlett.test(count ~ spray, data = InsectSprays) |
| } |
| \keyword{htest} |