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| Correlation > 1 between slope and qua... |
 
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I am trying to estimate a simple growth curve at 4 time points.
i s q | tot_pm1@0 tot_pm2@1 tot_pm3@2 tot_pm4@3;
This initial model ran the following two warnings:
WARNING: THE RESIDUAL COVARIANCE MATRIX (THETA) IS NOT POSITIVE DEFINITE.
WARNING: THE LATENT VARIABLE COVARIANCE MATRIX (PSI) IS NOT POSITIVE
DEFINITE.
For the first warning, I could see that the residual variance for the variable tot_pm1 was negative, but non-significant. So I constrained the residual variance to be 0.
This solved the first warning, but I still have the second warning.
Looking through the output I can see that the correlation between the slope and quadratic slope are correlated below -1.
I have read through a number of other threads to figure out how I can determine what might be causing this and how to solve it. Any advice you might have would be appreciated. |
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You can try correlating residuals of the outcome at adjacent timepoints, for example,
tot_pm1 WITH tot_pm2;
tot_pm2 WITH tot_pm3;
tot_pm3 WITH tot_pm4; |
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| Thank you Dr. Muthen. The issue is that I only have 2 df. How can I correlate the residuals in this way? Do you suggest freeing up df in some other way? |
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| Then you can free only two. |
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