% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/plots.R
\name{plot_pca_biplot}
\alias{plot_pca_biplot}
\title{Biplot of the first two residual components}
\usage{
plot_pca_biplot(fit)
}
\arguments{
\item{fit}{A fitted object from \code{\link{rasch}}.}
}
\value{
Called for its plotting side effect; invisibly \code{NULL}.
}
\description{
Item loadings on the first two residual principal components -- the pair
that usually carries any interpretable second dimension -- plotted against
one another on equal (isometric) axes. Items far from the origin with
opposing signs on PC1 mark a possible contrast, and PC2 separates them
further. Point colour follows the sign of the PC1 loading, the split the
unidimensionality t-test uses by default.
}
\examples{
set.seed(1)
d <- seq(-2, 2, length.out = 8)
X <- matrix(rbinom(500 * 8, 1, plogis(outer(rnorm(500), d, "-"))), 500, 8)
colnames(X) <- paste0("I", 1:8)
plot_pca_biplot(rasch(X))
}
