[R] Re: Tetrachoric and polychoric correlations, Polycor package

[David Duffy]

A bit late, but you might like to look at

http://www.qimr.edu.au/davidD/polyr.R

Regarding the original posters queries:

You can analyse polychoric correlations as if they were Pearson
correlations using standard software (eg sem), and this usually doesn't do
too badly, or go to AWLS (Browne) in LISREL etc, or ML analysis
of the full multidimensional contingency table using programs such as Mx,
or as you noted, mvtnorm (Mx uses Alan Genz's algorithms).

You can check model assumptions, and compare the results to those
from similar loglinear models.  For example, for a 3-way table, a single
factor model based on polychoric correlations should fit "perfectly", if
the no higher order interaction assumption is right,


| David Duffy (MBBS PhD)                                         ,-_|\
| email: davidD at qimr.edu.au  ph: INT+61+7+3362-0217 fax: -0101  /     *
| Epidemiology Unit, Queensland Institute of Medical Research   \_,-._/
| 300 Herston Rd, Brisbane, Queensland 4029, Australia  GPG 4D0B994A v