Twolevel CFA problems (identification... PreviousNext
Mplus Discussion > Multilevel Data/Complex Sample >
Message/Author
 Jeremy Miles posted on Tuesday, July 29, 2008 - 10:39 pm
Hi,

I'm doing a twolevel CFA, with teachers nested within schools, and I'm having a couple of problems.

First, I have a dichotomous variable indicating school type, middle school vs not middle school.

With variable in the model, I get the error:

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 -0.502D-18. PROBLEM INVOLVING PARAMETER 29.

(Where parameter 29 is the variance of this variable).

Even if there is nothing else in the model, I get this error.

My model looks like:

model:
%within%
%between%
midschool;
[midschool];


However, it appears that it is identified - at least, changing the starting values don't change the answers I get.

There's also a weird thing with the MIs, but I thought it would be clearer if that were in a separate post.
 Jeremy Miles posted on Tuesday, July 29, 2008 - 10:48 pm
The second part of that is the modification indices.

The modification indices suggest that the variable should be freed at the within level - and it has a fairly hefty MI. That's not possible, as it's a between variable

Minimum M.I. value for printing the modification index 5.000

M.I. E.P.C. Std E.P.C. StdYX E.P.C.

Within Level

Variances/Residual Variances

MIDSCHOO 1188.500 -1.000 -1.000 -1.000

Between Level


Beginning Time: 16:46:42
Ending Time: 16:46:42
Elapsed Time: 00:00:00


Is this something that should concern me?

Thanks,

Jeremy
 Linda K. Muthen posted on Wednesday, July 30, 2008 - 12:00 am
Please send the relevant files and your license number to support@statmodel.com.
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