mixed procedure question

Posted by Maguin, Eugene on
URL: http://spssx-discussion.165.s1.nabble.com/mixed-procedure-question-tp5740325.html

I ran the same multilevel model in mixed two different ways and received, no pun, mixed results.

This is the model statement for way 1. IL and TX are 0,1 variables and wave is three time points (0-3)

 

mixed total with wave tx il/fixed wave wave*wave tx

   wave*tx il wave*il tx*il wave*tx*il/

   print solution/random intercept wave | subject(rid) covtype(un).

 

Several of the effects are significant and since emmeans doesn’t play at all with covariates unless a “with” is used, I reversed-coded IL and TX and treated them as “by” variables in the way 2 version. When ran the model with the reversed variables I was startled to see some differences between the two results. The differences were in the Type III Tests of Fixed Effect table. Of the nine terms, including the intercept, six are different between the two model versions. Different in the denominator dof, F value, and significance values. But when I look at the Estimates of Fixed effects table: no differences, the same estimates, SEs, dfs, etc for both models. The same is true of the covariance parameters. Furthermore, the significance values in the Type III table and Estimates table correspond in the way 1 model but not so for the way 2 model using the reversed items and the “by” keyword.

 

I can’t make up plausible story for these differences. Can someone help me?

Thanks, Gene Maguin

 

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