Wed, 09/22/2010 - 15:08

I have a set of continuous measurements from MZ/DZ pairs, and data acquisition was done in two successive sessions. I am interested in estimating genetic, shared and unique environmental components. It seems an ACE model with repeated measurements would be appropriate here.

Is there any available example script for carrying out this kind of analysis with openMx?

This is one case in which the Cholesky model is actually interpretable as a model, rather than as a convenient trick to keep estimated matrices positive definite. See http://www.vipbg.vcu.edu/~vipbg/GE/GE_OpenMx.shtml for a relatively comprehensive multivariate twin script (it fits saturated models as well). Look for the section

# Fit Multivariate ACE Model with RawData and Matrices Input

# -----------------------------------------------------------------------

multiCholACEModel <- mxModel("multiCholACE",

for the so-called 'Triple Cholesky' model. Order your variables so that time1 is variable 1, and time2 is variable2. The magnitude of the A/C/E components specific to time 2 reflects the degree of new variance at time 2 not caused by factors operating at time 1.

Thanks to Hermine Maes for providing this resource!