Covariance matrix (psi) is not positi... PreviousNext
Mplus Discussion > Structural Equation Modeling >
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 Samuel Johnson posted on Friday, October 27, 2017 - 1:25 pm
Hello,

I am fitting a mediation model and get the following error.

WARNING: THE LATENT VARIABLE COVARIANCE MATRIX (PSI) IS NOT POSITIVE
DEFINITE. THIS COULD INDICATE A NEGATIVE VARIANCE/RESIDUAL VARIANCE FOR A
LATENT VARIABLE, A CORRELATION GREATER OR EQUAL TO ONE BETWEEN TWO LATENT
VARIABLES, OR A LINEAR DEPENDENCY AMONG MORE THAN TWO LATENT VARIABLES.
CHECK THE TECH4 OUTPUT FOR MORE INFORMATION.
PROBLEM INVOLVING VARIABLE c1.


THE STANDARD ERRORS OF THE MODEL PARAMETER ESTIMATES COULD NOT BE
COMPUTED. THE MODEL MAY NOT BE IDENTIFIED. CHECK YOUR MODEL.
PROBLEM INVOLVING THE FOLLOWING PARAMETER:
Parameter 99, c1 WITH c2

THE CONDITION NUMBER IS -0.645D-10.


Both c1 and c2 are independent variables (covariates). c1 is ordinal and c2 is binary. Both are declared categorical.

I checked the TECH4 output and found the following between c1 and c2:

ESTIMATED COVARIANCE MATRIX FOR THE LATENT VARIABLES: -0.401

ESTIMATED CORRELATION MATRIX FOR THE LATENT VARIABLES: -0.975


I examined the data and there is not any coding issues. Is there a way resolve the issue?
 Samuel Johnson posted on Friday, October 27, 2017 - 1:54 pm
As an update, I respecified the model and obtained the following in the TECH4 output between c1 and c2:


ESTIMATED COVARIANCE MATRIX FOR THE LATENT VARIABLES: -0.418

ESTIMATED CORRELATION MATRIX FOR THE LATENT VARIABLES: -1.028
 Bengt O. Muthen posted on Friday, October 27, 2017 - 2:13 pm
We need to see your output - please send to Support along with your license number.
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