Revision e71c994d653adbe4d49f0fed4cb9d80ae22d8ce1 authored by Roger Koenker on 24 June 2012, 00:00:00 UTC, committed by Gabor Csardi on 24 June 2012, 00:00:00 UTC
1 parent ff94aa3
predict.rq.Rd
\name{predict.rq}
\alias{predict.rq}
\alias{predict.rqs}
\alias{predict.rq.process}
\title{Quantile Regression Prediction}
\description{
Prediction based on fitted quantile regression model
}
\usage{
\method{predict}{rq}(object, newdata, type = "none", interval = c("none", "confidence"),
level = .95, na.action = na.pass, ...)
\method{predict}{rqs}(object, newdata, type = "Qhat", stepfun = FALSE, na.action = na.pass, ...)
\method{predict}{rq.process}(object, newdata, type = "Qhat", stepfun = FALSE, na.action = na.pass, ...)
}
\arguments{
\item{object}{ object of class rq or rqs or rq.process produced by \code{rq} }
\item{newdata}{An optional data frame in which to look for variables with
which to predict. If omitted, the fitted values are used.}
\item{interval}{type of interval desired: default is 'none', when set to
'confidence' the function returns a matrix predictions with point predictions
for each of the 'newdata' points as well as lower and upper confidence limits.}
\item{level}{converage probability for the 'confidence' intervals.}
\item{type}{For \code{predict.rq}, the method for 'confidence' intervals, if desired.
If 'percentile' then one of the bootstrap methods is used to generate percentile
intervals for each prediction, if 'direct' then a version of the Portnoy and Zhou
(1998) method is used, and otherwise an estimated covariance matrix for the parameter
estimates is used. Further arguments to determine the choice of bootstrap
method or covariance matrix estimate can be passed via the \dots argument.
For \code{predict.rqs} and \code{predict.rq.process} when \code{stepfun = TRUE},
\code{type} is either "Qhat" or "Fhat" depending on whether the user would
like to have estimates of the conditional quantile or distribution functions
respectively. As noted below such estimates can be monotonized with the function
\code{rearrange}.}
\item{stepfun}{If 'TRUE' return stepfunctions otherwise return matrix of predictions.
these functions can be estimates of either the conditional quantile or distribution
functions depending upon the \code{type} argument. When \code{stepfun = FALSE}
a matrix of point estimates of the conditional quantile function at the points
specified by the \code{newdata} argument. }
\item{na.action}{ function determining what should be done with missing values
in 'newdata'. The default is to predict 'NA'.}
\item{\dots}{ Further arguments passed to or from other methods.}
}
\details{
Produces predicted values, obtained by evaluating the quantile
regression function in the frame 'newdata' (which defaults to
'model.frame(object)'. These predictions purport to estimate
the conditional quantile function of the response variable of
the fitted model evaluated at the covariate values specified
in "newdata" and the quantile(s) specified by the "tau" argument.
Several methods are provided to compute confidence intervals for
these predictions.
}
\value{
A vector or matrix of predictions, depending upon the setting of
'interval'. In the case that there are multiple taus in \code{object}
when object is of class 'rqs' setting 'stepfun = TRUE' will produce a
\code{stepfun} object or a list of \code{stepfun} objects.
The function \code{rearrange} can be used to monotonize these
step-functions, if desired.
}
\references{
Zhou, Kenneth Q. and Portnoy, Stephen L. (1998)
Statistical inference on heteroscedastic models based on regression quantiles
Journal of Nonparametric Statistics, 9, 239-260
}
\author{R. Koenker}
\seealso{ \code{\link{rq}} \code{\link{rearrange}}}
\examples{
data(airquality)
airq <- airquality[143:145,]
f <- rq(Ozone ~ ., data=airquality)
predict(f,newdata=airq)
f <- rq(Ozone ~ ., data=airquality, tau=1:19/20)
fp <- predict(f, newdata=airq, stepfun = TRUE)
fpr <- rearrange(fp)
plot(fp[[2]],main = "Conditional Ozone Quantile Prediction")
lines(fpr[[2]], col="red")
legend(.2,20,c("raw","cooked"),lty = c(1,1),col=c("black","red"))
fp <- predict(f, newdata=airq, type = "Fhat", stepfun = TRUE)
fpr <- rearrange(fp)
plot(fp[[2]],main = "Conditional Ozone Distribution Prediction")
lines(fpr[[2]], col="red")
legend(20,.4,c("raw","cooked"),lty = c(1,1),col=c("black","red"))
}
\keyword{regression}
![swh spinner](/static/img/swh-spinner.gif)
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