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Cholesky_thresholds.R [6] | 14.62 KB |
myFunctions.R [7] | 3.44 KB |
Dear all,
I would like to fit a trivariate Cholesky model in OpenMx. I have data of twins aged 7, 10, and 12 years old with longitudinal data for a part of the sample. My data are skewed, so I made three categories and I would like to fit a threshold model on them. I fixed the thresholds to be equal across ages, so I estimate two thresholds in total. The means and the variances of the phenotype increase with age though, so I would like to fix the mean at time point 1 to zero and the variance to one and freely estimate the means and variances of the subsequent ages. There are also quantitative and qualitative sex differences. When I run the script that is attached to this posting, I keep getting the following warning message:
Running CholACE
Warning message:
In model 'CholACE' Optimizer returned a non-zero status code 6. The model does not satisfy the first-order optimality conditions to the required accuracy, and no improved point for the merit function could be found during the final linesearch (Mx status RED)
I have changed the starting values many times and each time I get a different -2LL and totally different path estimates. I thought that there might be too few observations in some of the cells (especially for the longitudinal data), however the model does not run on simulated data either (see script).
There is no problem when I run univariate threshold models for each age separately.
Does anyone know what is going wrong here? Could it be that the variances need to be one for all ages?
Many thanks in advance!
Best regards
Charlotte