Help!
I'm constantly hoping that SPSS will evolve to allow for MIXED model contrasts before another PI presents with data that have primary aims involving longitudinal analyses with contrasts, but SPSS does not seem to be getting more flexible in this area.
Here's my scenario: We have a data set with 4 time points and 4 treatment groups and we are interested in the linear "GROUP by TIME" effect for each of the following GROUP contrasts:
GROUP Contrast(1) -.5 -.5 0 1
GROUP Contrast(2) -.5 .5 -.5 .5
GROUP Contrast(3) .5 -.5 -.5 .5
I've tried many models- and this is the closest I can get:
MIXED OUTCOME BY GROUP WITH TIME
/FIXED GROUP TIME GROUP*TIME
/test= GROUP -1 -1 0 2
/test=GROUP -1 1 -1 1
/test= GROUP 1 -1 -1 1
/random intercept | subject (ID) /print solution testcov cps r g
/SAVE PRED.
However, the contrast estimates seem to be based on the GROUP effect and not the linear GROUP by TIME effect, which is what is of interest.
Can you either advise me or direct me to a good resource on this type of model?
Thanks!
Charla Nich
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