\name{crit}
\alias{crit}
\alias{crit<-}
\title{
Compute critical values for confidence intervals.
}
\usage{
crit(fit, const=c(0, 1), d=1, cov=0.95, rdf=0)
crit(fit) <- value
}
\arguments{
\item{fit}{\code{"locfit"} object. This is optional; if a fit is
  provided, defaults for the other arguments are taken from the critical
  value currently stored on this fit, rather than the usual values above.
  \code{crit(fit)} with no other arguments will just return the current
  critical value.}
\item{const}{Tube formula constants for simultaneous bands (the default,
  \code{c(0,1)}, produces pointwise coverage). Usually this is generated
  by the \code{\link{kappa0}} function and should not be provided by the
  user.}
\item{d}{Dimension of the fit. Again, users shouldn't usually provide
  it.}
\item{cov}{Coverage Probability for critical values.}
\item{rdf}{Residual degrees of freedom. If non-zero, the critical values
  are based on the Student's t distribution. When \code{rdf=0}, the
  normal distribution is used.}
\item{value}{Critical value object generated by \code{\link{crit}} or
  \code{\link{kappa0}}.}
}
\description{
  Every \code{"locfit"} object contains a critical value object to be used in
  computing and ploting confidence intervals. By default, a 95\% pointwise
  confidence level is used. To change the confidence level, the critical
  value object must be substituted using \code{\link{crit}} and
  \code{\link{crit<-}}.
}
\value{
  Critical value object.
}
\seealso{
\code{\link{locfit}}, \code{\link{plot.locfit}},
\code{\link{kappa0}}, \code{\link{crit<-}}.
}
\examples{
# compute and plot 99\% confidence intervals, with local variance estimate.
data(ethanol)
fit <- locfit(NOx~E,data=ethanol)
crit(fit) <- crit(fit,cov=0.99)
plot(fit,band="local")

# compute and plot 99\% simultaneous bands
crit(fit) <- kappa0(NOx~E,data=ethanol,cov=0.99)
plot(fit,band="local")
}
%\keyword{locfit}
\keyword{smooth}
% Converted by Sd2Rd version 0.2-a5.