https://github.com/cran/eRm
Tip revision: 453534604193145d7719a4267a0c53946f5c553b authored by Patrick Mair on 06 December 2013, 00:00:00 UTC
version 0.15-3
version 0.15-3
Tip revision: 4535346
plotDIF.Rd
\name{plotDIF}
\alias{plotDIF}
\title{
Confidence intervals plot of item parameter estimates.
}
\description{
Performs an plot of item parameter conficence intervals based on \code{LRtest} subgroup splitting.
}
\usage{
plotDIF(object, item.subset = NULL, gamma = 0.95, main = NULL,
xlim = NULL, xlab = " ", ylab=" ", col = NULL,
distance, splitnames=NULL, leg = FALSE, legpos="bottomleft", ...)
}
\arguments{
\item{object}{
An object of class \code{LR} (if more objects should be plotted, the argument has to be defined as a \code{list}).
}
\item{item.subset}{
Subset of items to be plotted. Either a numeric vector indicating the items or a character vector indicating the itemnames.
If nothing is defined (default), all items are plotted.
}
\item{gamma}{
The level for the item parameter's confidence limits (default is gamma = 0.95).
}
\item{main}{
Main title for the plot.
}
\item{xlim}{
Numeric vector of length 2, giving the x coordinates ranges of the plot (the y coordinates depend on the number of
depicted items).
}
\item{xlab}{
Label for the x axis.
}
\item{ylab}{
Label for the y axis.
}
\item{col}{
By default the color for the drawn confidence lines is determined automatically whereas every group (split criterion)
is depicted in the same color.
}
\item{distance}{
Distance between each item's confidence lines -- if omitted, the distance shrinks with increasing numbers of split criteria. Can be overriden using values in (0, 0.5).
%Distance between the drawn confidence lines, default is division by factor 10 .
}
\item{splitnames}{
For labeling the splitobjects in the legend (returns a nicer output).
}
\item{leg}{
If \code{TRUE} a legend is provided by default.
}
\item{legpos}{
Position of the legend with possible values \code{"bottomright"}, \code{"bottom"}, \code{"bottomleft"}, \code{"left"},
\code{"topleft"}, \code{"top"}, \code{"topright"}, \code{"right"} and \code{"center"}. The default value for the legend
is \code{"bottomleft"}.
}
\item{...}{
Further options to be passed to \code{plot}.
}
}
\details{
If there are items that cannot be estimated for some reasons, certainly these ones are not plotted.
For plotting several objects of class \code{LR}, the subgroup splitting by \code{LRtest} has to
be carried out for the same data set (or at least item subsets of it).
Plotting a certain subset of items could be useful if the objects of class \code{LR} contain a huge number
of estimated items.
The default level for the conficence limits is gamma = 0.95. (If the conficence limits should be
corrected it is useful to use a correction, e.g., Bonferroni: 1 - (1 - gamma) / number of estimated items.)
}
\value{
\code{plotCI} returns a list containing the confidence limits of each group in each \code{LRtest} object.
}
\author{
Kathrin Gruber, Reinhold Hatzinger
}
\seealso{\code{\link{LRtest}}, \code{\link{confint.threshold}}, \code{\link{thresholds}}}
\examples{
# the object used is the result of running RM(raschdat1)
res <- raschdat1_RM_fitted # see ? raschdat1_RM_fitted
\dontrun{
# LR-test on dichotomous Rasch model with user-defined split
splitvec <- rep(1:2, each = 50)
lrres <- LRtest(res, splitcr = splitvec)
# LR-test with mean split
lrres2 <- LRtest(res, split = "mean")
# combination of LRtest-objects in a list
RMplotCI <- list(lrres, lrres2)}
# the object raschdat1_RM_plotDIF is the result of the computations outlined
# above and is loaded to save computation time. see ?raschdat1_RM_plotDIF
RMplotCI <- raschdat1_RM_plotDIF
# Confidence intervals plot with default assumptions
plotDIF(RMplotCI)
# Confidence intervals plot with Bonferroni correction
plotDIF(RMplotCI, gamma = (1 - (0.05/10)))
# Confidence intervals plot for an item subset
plotDIF(RMplotCI, item.subset = 1:6)
# with user defined group color and legend
plotDIF(RMplotCI, col = c("red", "blue"), leg = TRUE, legpos = "bottomright")
# with names for the splitobjects
plotDIF(RMplotCI, col = c("red", "blue"), leg = TRUE, legpos = "bottomright",
splitnames = c(paste("User", 1:2), paste(rep("Mean", 2), 1:2)))
}
\keyword{models}