poly.mat: Find polychoric correlations of item data
Description
Uses John Fox's hetcor function (from polychor package) to find a matrix of polychoric correlations for integer data. Essentially a wrapper for hetcor to convert integer item data into factor (categorical) data and then use hetcor. Just a useful shortcut for subsequent factor analysis.
Usage
poly.mat(x, short = TRUE, std.err = FALSE, ML = FALSE)
Arguments
x
A matrix or data frame of integer data
short
short=TRUE, just show the correlations, short=FALSE give the full hetcor output
std.err
std.err=FALSE does not report the standard errors (faster)
ML
ML=FALSE do a quick two step procedure, ML=TRUE, do longer maximum likelihood
Value
A matrix of polychoric correlations (if short=TRUE), otherwise a list of various estimates (see hetcor).
Details
Typical personality and item data are integer values (0,1 for ability; 1,2, 3, 4 for attitude scales). The normal correlation procedures will find Pearson correlations (cor). The polycor and hetcor functions from John Fox's polychor package will find polychoric correlations for categorical data. This wrapper function converts integer data to categorical data and then calls hetcor.