https://github.com/cran/eRm
Tip revision: 2216207892d8045caec2e1010f59605136dd7435 authored by patrick.mair on 14 October 2006, 00:00:00 UTC
version 0.3.1
version 0.3.1
Tip revision: 2216207
PCM.Rd
\name{PCM}
\alias{PCM}
%- Also NEED an '\alias' for EACH other topic documented here.
\title{Estimation of partial credit models}
\description{
This function computes the parameter estimates of a partial credit model for polytomous
item responses by using CML estimation. }
\usage{
PCM(X, W)
}
%- maybe also 'usage' for other objects documented here.
\arguments{
\item{X}{Input data matrix or data frame with item responses (starting from 0); rows represent individuals, columns represent items.}
\item{W}{Design matrix for the PCM. If omitted, the function will compute W automatically.}
}
\details{
Through specification in W, the parameters of the categories with 0 responses
are set to 0 as well as the first category of the first item. Available methods
for PCM-objects are \code{print}, \code{coef}, \code{model.matrix},
\code{vcov}, \code{plot}, \code{summary}.
}
\value{
Returns an object of class \code{Rm} and contains the log-likelihood value,
the parameter estimates and their standard errors.
\item{model}{Type of model.}
\item{loglik}{The log-likelihood.}
\item{df}{Degrees of freedom.}
\item{iter}{Number of iterations required.}
\item{etapar}{Estimated basic item parameters.}
\item{se_eta}{Standard errors of the estimated basic item parameters.}
\item{hessian}{Hessian matrix.}
\item{betapar}{Estimated item parameters.}
\item{LR}{The log-likelihood test statistic for the model.}
\item{W}{Design matrix.}
\item{etaparG1}{Parameters for first LR-group.}
\item{etaparG2}{Parameters for second LR-group.}
}
\references{
Fischer, G. H., and Molenaar, I. (1995). Rasch Models - Foundations,
Recent Developements, and Applications. Springer.
}
\author{Patrick Mair, Reinhold Hatzinger}
\note{Missing Values are not allowed in X, the category coding must start with 0 (lowest category).
}
\seealso{\code{\link{print.eRm}},\code{\link{coef.eRm}},\code{\link{vcov.eRm}},\code{\link{model.matrix.eRm}},\code{\link{plot.Rm}},
\code{\link{summary.eRm}}}
\examples{
#PCM with 10 subjects, 3 items
data(pcmdat)
res <- PCM(pcmdat)
res
}
\keyword{models}