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Hi Stuart, hope all is well! > > Is there any way to examine an interaction of > group with covariate at the second level? > > I want to examine the interaction of depression > ratings with my contrast images and group but > there does not seem to be any way to do this... > But there are. The "easy" way would be to use a "PET-models->Single subject: Conditions and Covariates" analysis where you enter group as your conditions and your depression ratings as your covariate. Then chose "Center around condition means" and "Interaction with condition". The "problem" with that approach is the masking, which will not work so well on your contrast images. The "slightly trickier" way would be to use the "Multiple regression" option in "Basic models". It really wouldn't be too hard for you to create the appropriate regressors to implement your model, but you could also "cheat" a little. Run the analysis I suggested above. Disregard the results, EXCEPT the SPMcfg.mat file which you load into matlab while still running SPM. Now do the "Basic models->Multiple regression" and enter the columns of xX.X (which was contained in SPMcfg.mat) as your regressors. That way all the "centering stuff" is automatically taken care of for you and there is less risk of mistakes. Good luck Jesper