hi Donald

We collected data from participants who perfomed the same task in two sessions a week apart.  We would like to compare the PPI effect between these sessions.  Would you recommend performing the PPI for the two sessions individually and then contrasting them at the second level, or putting everything in the same model and using P.ConcatR?

thanks

James

James,

As it seems you want to compare the two sessions (2 weeks apart), you don't want to use the ConcatR=1 option. The concatR=1 option combines all regressors that have the same name. Thus, since time points would have the same task name, the regressors would be collapsed and you wouldn't be able to compare the sessions that are 2 weeks apart.

Hope this helps.

hi Donald

Thanks for your quick response!  So just to be clear, do you think it would be vaiid to run a separate analysis for each session and then contrast the betas at the second level?  As the participants are doing the same thing, we just want to know whether the network supporting carrying out the task is the same in both sessions or whether something changes.  Can you suggest a better way if this does not seem valid to you?

James