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Twolevel CFA problems (identification... |
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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. |
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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 |
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