-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of David Duffy
Sent: Thursday, December 09, 2004 1:29 AM
To: r-help at stat.math.ethz.ch
Subject: [R] Re: Tetrachoric and polychoric correlations,
Polycor package
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