Basic idea is: to specify dummy covariates (“0” or “1”) in the “hetres_pos” option.
In this example, we will consider 3 different residual variances by class in a single-trait model. We need extra 3 columns in the data file. Each column contains the following information:
extra column 1: "1" if this observation is related to the residual variance 1; else "0". extra column 2: "1" if this observation is related to the residual variance 2; else "0". extra column 3: "1" if this observation is related to the residual variance 3; else "0".
We assume these columns are corresponding to 6-th, 7-th, and 8-th columns in the data file, respectively.
The following lines should be added to your parameter file:
OPTION hetres_pos 6 7 8 OPTION hetres_pol 20.0 20.0 20.0
An initial value should be specified as the natural logarithm of the variance. For example, 20.0 means ln(20) = 3.