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P value of 1 in mxCompare

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Lisa M's picture
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Joined: 08/19/2013 - 04:02
P value of 1 in mxCompare
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Hello,
I am working on an analysis of a univariate sex limitation model for depression and I have run into a potential problem. When comparing the homogeneity ACE model to the AE model, I get a p-value of 1 in mxCompare. The fit of the models are very similar:

> mxCompare(HomACEModelFit,HomAEModelFit)
    base           comparison   ep   minus2LL      df          AIC        diffLL                 diffdf      p
1 HomACE       <NA>            4     16217.9      21258   -26298.1   NA                     NA       NA
2 HomACE      HomAE           3    16217.9       21259   -26300.1 -1.426603e-05    1         1

Does this mean there is something wrong with the models, or is open mx rounding off the value? When I compare them to the full heterogeneity model it works fine and I get p values of 0.20 and 0.12.
Due to confidentiality reasons I am not able to include the data but I have attached the script for the models.
Any input would be greatly appreciated,
Kind regards/
Lisa

mhunter's picture
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Joined: 07/31/2009 - 15:26
The difference in log

The difference in log likelihoods is on the order of 1e-5. The p-value associated with this will be essentially one.

> pchisq(1.426603e-05, df=1, lower.tail=FALSE)
[1] 0.9969864
Lisa M's picture
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Joined: 08/19/2013 - 04:02
Thank you so much for the

Thank you so much for the quick response!

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