analysing cognitive rehabilitation and controlling for spontaneous recovery(SEM)

Dear all,

When trying to figure out the proportion of explained variance of a cognitive rehabilitation program for stroke patients, you have to control for any progress by spontaneous recovery and diaschisis right? So if we measure progress without a cognitive rehabilitation program, you get to see how much this sample on average is progressing, cognitively right(waitlist condition)?

So the waitlist condition gives information about progress without the rehabilitation program and the experimental group gives information about the progress with the rehabilitation program. of course not all the progress in the experimental group can be accounted for by the rehabilitation program.

The problem is, the waitlist and experimental condition are two different groups. Therefore, the amount of cognitive improvement withouth the rehabilitation program is not measured in the group who will get the rehabilitation program. It would be nice to know how much of the variance is actually explained by the training when the effect of spontaneous recovery if substracted.

Especially when constructing a model using SEM, it would be good to incorporate this waitlist variable.

Do any of you guys have thoughts and ideas for this issue?

Thanks in advance for your help!

Kind regards