Re: mixed procedure question

Posted by Bruce Weaver on
URL: http://spssx-discussion.165.s1.nabble.com/mixed-procedure-question-tp5740325p5740326.html

Hi Gene.  If I follow what you're doing, you're missing some terms.  If you
treated all 3 of your variables as categorical (i.e., had them follow BY),
and if you included all 2- and 3-way interactions, you would eat up 11 df
(if I counted correctly).  So when you treat them as continuous (following
WITH), and include polynomial terms where there are 2 or more categories,
then you still need 11 df.  And I think you are missing a couple of terms.
I reckon you need all of the following terms in your model (with W standing
for Wave):

IL
TX
W
W*W
IL*TX
IL*W
IL*W*W
TX*W
TX*W*W
IL*TX*W
IL*TX*W*W

You have only these 8 terms:

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

The 3 you are missing are the ones that involve the quadratic component of
the interactions with Wave:

IL*W*W
TX*W*W
IL*TX*W*W

By the way, you said Wave has 3 levels, but then said 0-3.  Did you mean
0-2?  I assumed you did.

HTH.
Bruce



Maguin, Eugene wrote

> 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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