Covariates with zero variance in LCGA PreviousNext
Mplus Discussion > Latent Variable Mixture Modeling >
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 Sheila Frankfurt posted on Sunday, April 03, 2011 - 2:46 pm
Variable: names are id bsidep1 bsidep2 bsidep3 bsidep4 x1 x2 x3;
usevar = bsidep1-bsidep4 x1 x2;
missing = all (999);
CLASSES = c(4);
SAVEDATA: FILE IS dep_4q_x1x2_output;
save=cprobabilities;
Analysis: type = MIXTURE missing;
STARTS = 1000 300;
STITERATIONS = 20;
Model: %OVERALL%
i s q| bsidep1@0 bsidep2@1.5 bsidep3@5.5 bsidep4@11.5;
i-q@0;
c#1 ON x1 x2;
c#2 ON x1 x2;
c#3 ON x1 x2;
Output: sampstat standardized tech1 tech11 tech14;

This model runs fine, but I get this error message:

WARNING: THE SAMPLE VARIANCE OF X1 IN CLASS 2 IS 0.000. (the same for X2-sf)

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:
23 22

This was the gamma parameters for class 2 on to x1 and x2. Does fixing the regression coefficient of the latent construct (class) on to the exogenous variable (x1 and x2) make this model uninterpretable?
 Linda K. Muthen posted on Monday, April 04, 2011 - 2:59 pm
This is not a problem. It just tells you that all members of class 2 have the same value for x1.
 Sheila Frankfurt posted on Monday, April 04, 2011 - 10:53 pm
Great, thank you very much!
---Sheila
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