Re: Mixed Model Repeated Measures

Posted by Ryan on May 15, 2014; 12:35am
URL: http://spssx-discussion.165.s1.nabble.com/Mixed-Model-Repeated-Measures-tp5726021p5726052.html

Gene,

Run the code below and you will see that the main-diagonal elements of the residual covariance matrix are estimated using all possible data for each group by comparing the residual variance estimates from MIXED to the group-specific variances from MEANS.

HTH.

Ryan

--

*Generate Data.
set seed 65923454.

new file.
input program.
compute subject=-99.
compute group = -99.
leave subject to group.
loop subject= 1 to 1000.
loop group = 1 to 3.
compute y = rv.normal(0,1).
end case.
end loop.
end loop.
end file.
end input program.
execute.

USE ALL.
COMPUTE filter_$=(uniform(1)<=.95).
VARIABLE LABELS filter_$ 'Approximately 95% of the cases (SAMPLE)'.
FORMATS filter_$ (f1.0).
FILTER  BY filter_$.
EXECUTE.

IF  (filter_$=0) y=$SYSMIS.
EXECUTE.

delete variables filter_$.

 MIXED y BY group
   /FIXED=group  | SSTYPE(3)
   /METHOD=REML
   /PRINT=R
   /REPEATED=group | SUBJECT(subject) COVTYPE(diag).

MEANS TABLES=y BY group
  /CELLS=VAR COUNT.

On Wed, May 14, 2014 at 10:48 AM, Maguin, Eugene <[hidden email]> wrote:

Alex,

Thank you for setting me straight. A followup question.

Does this imply that the within vcv matrix may have different Ns for different elements?

I understand (or think I do) the computation implications of ‘all available data points’ in a growth curve model, but I don’t for a repeated measures.

Thanks, Gene Maguin

 

From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of Alex Reutter
Sent: Wednesday, May 14, 2014 10:25 AM
To: [hidden email]
Subject: Re: Mixed Model Repeated Measures

 

This statement:
"
I may be wrong about this because I haven't run a repeated measures analysis with mixed on a dataset with missing data but my bet is that cases with missing data are going to be excluded. Your repeated statement will be something exactly like
Repeated visit | subject(people) covtype(??).
Thus each people will be expected to have 72 visit data points.
"

Would be true when running GLM, but not MIXED.  MIXED and GENLINMIXED use all available visit data points.

Alex