HOW do I insert a baseline covariate in repeated GLM?

mieri

New Member
#1
Am I doing something wrong?

Using repeated GLM.
Two groups, experiment and control.
Dependent is a score on a scale.
Data (the same score on the scale) are collected pre intervention and two post-tests.
I am going to use the pre-test scores as a covariate to correct for possible differences at pre-test between the two groups.

In SPSS, repeated measures, I insert the three data collection points (pre - post1 -post2) as within subject. When I want to insert the pre-test as covariate - it is not in the list since it is now in the "within subjects box". Am I doing something really wrong in trying this? Or is there a solution?

Can't figure this out! Help is appreciated!