Problem recreating optimal model PreviousNext
Mplus Discussion > Latent Variable Mixture Modeling >
 Jon Heron posted on Friday, September 29, 2006 - 10:52 am

I think I may have found a problem and although I need to run a few more checks on this, I thought I'd post my findings to see if anyone else has found the same.

I've been running a 5-class LCA on 5 time points (binary vars) and a sample of 10,000 using the 'noserr' and 'nochi' options to improve running time.

In the most recent run I used
starts = 20000 10000;
stiterations = 10;
stscale = 20;
(just to be doubly sure).

I've been finding that the optimal model is repeated with a good number of starting values but that using the optseed option will not recreate the model which appears as optimal.

After much headscratching I think this is due to the 'noserr' option. With this turned off I am presented with a warning about positive definite matrices and hence it seems quite clear to me why the optseeds are not doing their job.

Like I say, this is still work in progress. It may turn out to be nothing to do with 'noserr', but either way I have something strange going on here.
 Scott Weaver posted on Friday, September 29, 2006 - 3:41 pm
Hi Jon,

I have perhaps experienced this same issue. I wrote to Mplus support and was informed that I need to specify the same STSCALE that was used to obtain the optimal solution. What I had done was when I specified OPTSEED, I deleted the STSCALE line - and thus it defaulted to a value of 5.

So if you add STSCALE=20 next to your OPTSEED command, you might fix your problem.

 Bengt O. Muthen posted on Sunday, October 01, 2006 - 6:39 pm
I agree with Scott's suggestion. Let us know if that does not resolve it.
 Jon Heron posted on Monday, October 02, 2006 - 7:57 am
Sounds quite plausible as I turn off the various 'st' options when I use OPTSEED.

Thanks for this, I'll let you know how I get on.

 Jon Heron posted on Tuesday, October 03, 2006 - 7:23 am
All working now - thanks for the suggestion.

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