LCA: help interpreting output/errors
Message/Author
 Brian Hall posted on Tuesday, September 21, 2010 - 5:27 am
Performing a LCA on a sample of 350 with 4 measures. Please help in interpreting these error messages. Also please provide a simple explanation for the application of random starts.
Brian

1:
IN THE OPTIMIZATION, ONE OR MORE LOGIT THRESHOLDS APPROACHED AND WERE SET AT THE EXTREME VALUES. EXTREME VALUES ARE -15.000 AND 15.000.
THE FOLLOWING THRESHOLDS WERE SET AT THESE VALUES:
* THRESHOLD 1 OF CLASS INDICATOR var1 FOR CLASS 2 AT ITERATION 7
* THRESHOLD 1 OF CLASS INDICATOR var1 FOR CLASS 3 AT ITERATION 11
* THRESHOLD 1 OF CLASS INDICATOR var1 FOR CLASS 1 AT ITERATION 19
* THRESHOLD 1 OF CLASS INDICATOR

2:
THE STANDARD ERRORS OF THE MODEL PARAMETER ESTIMATES MAY NOT BE
TRUSTWORTHY FOR SOME PARAMETERS DUE TO A NON-POSITIVE DEFINITE
FIRST-ORDER DERIVATIVE PRODUCT MATRIX. THIS MAY BE DUE TO THE STARTING
VALUES BUT MAY ALSO BE AN INDICATION OF MODEL NONIDENTIFICATION. THE
CONDITION NUMBER IS 0.174D-14. PROBLEM INVOLVING PARAMETER 4.

3)
ONE OR MORE MULTINOMIAL LOGIT PARAMETERS WERE FIXED TO AVOID SINGULARITY
OF THE INFORMATION MATRIX. THE SINGULARITY IS MOST LIKELY BECAUSE THE
MODEL IS NOT IDENTIFIED, OR BECAUSE OF EMPTY CELLS IN THE JOINT
DISTRIBUTION OF THE CATEGORICAL LATENT VARIABLES AND ANY INDEPENDENT VARIABLES. THE FOLLOWING PARAMETERS WERE FIXED: 19
 Linda K. Muthen posted on Tuesday, September 21, 2010 - 6:44 am
1. This is not a problem. It means that the thresholds are high reflecting probabilities of 0 (+15) and 1 (-15). This can be helpful in defining the classes.

2. You would need to send the output and your license number to support@statmodel.com for this. The meaning can vary.

3. This is usually because in one class the covariate has no variability but I would have to see it to be sure.