\Header{fligner.test}{Fligner-Killeen Test for Homogeneity of Variances}
\keyword{htest}{fligner.test}
\begin{Description}\relax
Performs a Fligner-Killeen (median) test of the null that the
variances in each of the groups (samples) are the same.\end{Description}
\begin{Usage}
\begin{verbatim}fligner.test(x, g)\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] a numeric vector of data values, or a list of numeric data
vectors.
\item[\code{g}] a vector or factor object giving the group for the
corresponding elements of \code{x}.
Ignored if \code{x} is a list.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
If \code{x} is a list, its elements are taken as the samples to be
compared for homogeneity of variances, and hence have to be numeric
data vectors.  In this case, \code{g} is ignored, and one can simply
use \code{fligner.test(x)} to perform the test.  If the samples are
not yet contained in a list, use \code{fligner.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}.

The Fligner-Killeen (median) test has been determined in a simulation
study as one of the many tests for homogeneity of variances which is
most robust against departures from normality, see Conover, Johnson \&
Johnson (1981).  It is a k-sample simple linear rank which uses the
ranks of the absolute values of the centered samples and weights
\eqn{a(i) = qnorm((1 + i/(n+1))/2)}{}.  The version implemented here
uses median centering in each of the samples (F-K:med \eqn{X^2}{} in the
reference).\end{Details}
\begin{Value}
A list of class \code{"htest"} containing the following components:
\begin{ldescription}
\item[\code{statistic}] the Fligner-Killeen:med \eqn{X^2}{} test statistic.
\item[\code{parameter}] the degrees of freedom of the approximate chi-square
distribution of the test statistic.
\item[\code{p.value}] the p-value of the test.
\item[\code{method}] the string
\code{"Fligner-Killeen test for homogeneity of variances"}.
\item[\code{data.name}] a character string giving the names of the data.
\end{ldescription}
\end{Value}
\begin{References}\relax
W. J. Conover \& Mark E. Johnson \& Myrie M. Johnson (1981).
A comparative study of tests for homogeneity of variances, with
applications to the outer continental shelf bidding data.
\emph{Technometrics} \bold{23}, 351--361.\end{References}
\begin{SeeAlso}\relax
\code{\Link{ansari.test}} and \code{\Link{mood.test}} for rank-based
two-sample test for a difference in scale parameters;
\code{\Link{var.test}} and \code{\Link{bartlett.test}} for parametric
tests for the homogeneity of variances.\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
data(InsectSprays)
plot(InsectSprays$count ~ InsectSprays$spray)
fligner.test(InsectSprays$count, InsectSprays$spray)
## Compare this to bartlett.test()
\end{ExampleCode}
\end{Examples}

