| % File src/library/stats/man/var.test.Rd |
| % Part of the R package, https://www.R-project.org |
| % Copyright 1995-2007 R Core Team |
| % Distributed under GPL 2 or later |
| |
| \name{var.test} |
| \alias{var.test} |
| \alias{var.test.default} |
| \alias{var.test.formula} |
| \title{F Test to Compare Two Variances} |
| \description{ |
| Performs an F test to compare the variances of two samples from normal |
| populations. |
| } |
| \usage{ |
| var.test(x, \dots) |
| |
| \method{var.test}{default}(x, y, ratio = 1, |
| alternative = c("two.sided", "less", "greater"), |
| conf.level = 0.95, \dots) |
| |
| \method{var.test}{formula}(formula, data, subset, na.action, \dots) |
| } |
| \arguments{ |
| \item{x, y}{numeric vectors of data values, or fitted linear model |
| objects (inheriting from class \code{"lm"}).} |
| \item{ratio}{the hypothesized ratio of the population variances of |
| \code{x} and \code{y}.} |
| \item{alternative}{a character string specifying the alternative |
| hypothesis, must be one of \code{"two.sided"} (default), |
| \code{"greater"} or \code{"less"}. You can specify just the initial |
| letter.} |
| \item{conf.level}{confidence level for the returned confidence |
| interval.} |
| \item{formula}{a formula of the form \code{lhs ~ rhs} where \code{lhs} |
| is a numeric variable giving the data values and \code{rhs} a factor |
| with two levels giving 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{ |
| The null hypothesis is that the ratio of the variances of the |
| populations from which \code{x} and \code{y} were drawn, or in the |
| data to which the linear models \code{x} and \code{y} were fitted, is |
| equal to \code{ratio}. |
| } |
| \value{ |
| A list with class \code{"htest"} containing the following components: |
| \item{statistic}{the value of the F test statistic.} |
| \item{parameter}{the degrees of the freedom of the F distribution of |
| the test statistic.} |
| \item{p.value}{the p-value of the test.} |
| \item{conf.int}{a confidence interval for the ratio of the population |
| variances.} |
| \item{estimate}{the ratio of the sample variances of \code{x} and |
| \code{y}.} |
| \item{null.value}{the ratio of population variances under the null.} |
| \item{alternative}{a character string describing the alternative |
| hypothesis.} |
| \item{method}{the character string |
| \code{"F test to compare two variances"}.} |
| \item{data.name}{a character string giving the names of the data.} |
| } |
| \seealso{ |
| \code{\link{bartlett.test}} for testing homogeneity of variances in |
| more than two samples from normal distributions; |
| \code{\link{ansari.test}} and \code{\link{mood.test}} for two rank |
| based (nonparametric) two-sample tests for difference in scale. |
| } |
| \examples{ |
| x <- rnorm(50, mean = 0, sd = 2) |
| y <- rnorm(30, mean = 1, sd = 1) |
| var.test(x, y) # Do x and y have the same variance? |
| var.test(lm(x ~ 1), lm(y ~ 1)) # The same. |
| } |
| \keyword{htest} |