LCGA and singular matrix PreviousNext
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 Gareth posted on Tuesday, August 11, 2009 - 10:16 am
I am running a LCGA, progressively increasing the number of latent classes from 2 to 8. The BIC value continues to decrease, until I get "ONE OR MORE PARAMETERS WERE FIXED TO AVOID SINGULARITY OF THE INFORMATION MATRIX" with the 8-class solution.

When Mplus fixes a parameter to avoid a singular, can the BIC values and other parts of the model be trusted? Is this an indication that there are too many classes, even though the BIC has not increased yet?
 Linda K. Muthen posted on Wednesday, August 12, 2009 - 9:01 am
With LCGA, BIC can continue to decrease without hitting a minimum. You may find that GMM is better for your data in this case.

See also the following paper which is available on the website. It gives suggestions for determining the number of classes using measures other than BIC:

Nylund, K.L., Asparouhov, T., & Muthen, B. (2007). Deciding on the number of classes in latent class analysis and growth mixture modeling. A Monte Carlo simulation study. Structural Equation Modeling, 14, 535-569.

Results can be trusted when parameters are fixed unless this is done because of non-identification.
 Yannan Gao posted on Monday, October 12, 2020 - 10:36 am
Hi Dr. Muthen,

I just want to follow up on your comment: I got the same error message but it also says "THE SINGULARITY IS MOST LIKELY BECAUSE THE MODEL IS NOT IDENTIFIED, OR BECAUSE OF EMPTY CELLS IN THE JOINT DISTRIBUTION OF THE CATEGORICAL VARIABLES IN THE MODEL." How can I find out which of the two possibility caused the singularity?

The model I'm running is LCGA with ordinal variables. I found out in TECH1 output that the parameters that were fixed are class-specific intercepts. So I wanted to decide if I can still use the solution in this case.
 Bengt O. Muthen posted on Monday, October 12, 2020 - 12:02 pm
We have to see your full output to diagnose this - send to Support along with your license number.
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