Negative Variances in Bifactor Modeling PreviousNext
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 Seth J. Schwartz posted on Wednesday, June 25, 2014 - 4:52 pm
Dear Bengt and Linda:

My post-doc and I are running some bifactor models and are getting one negative residual variance.

Our input looks like this:

ANALYSIS:
ESTIMATOR IS MLR;
Type is Complex; !School is the clustering variable;
ITERATIONS = 10000000;

MODEL:
ASrch by AAIM01_1* AAIM02_1 AAIM04_1 AAIM08_1 AAIM10_1;
ACom by AAIM03_1* AAIM05_1 AAIM06_1 AAIM07_1 AAIM09_1
AAIM11_1 AAIM12_1;
General by AAIM01_1* AAIM02_1 AAIM03_1 AAIM04_1 AAIM05_1
AAIM06_1 AAIM07_1 AAIM08_1 AAIM09_1 AAIM10_1
AAIM11_1 AAIM12_1;

ASrch@1;
ACom@1;
General@1;

General with ACom@0 ASrch@0;


The variance for AAIM12_1 is negative and significant. Should we set the negative variance to zero? Is that OK to do?

Thanks so much.

Seth Schwartz
 Linda K. Muthen posted on Wednesday, June 25, 2014 - 8:18 pm
You should not fix a significant negative residual variance to zero. This calls for a change in the model.
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