I want to test whether the correlation between brain activity and a behavioral score is different between two groups. I tried to do this with a 2-sample t test and adding the two behavioral scores as covariates for each group separately and then using a contrast 1 -1 over the covariates. However, I got the this error message:

Running job #2

------------------------------------------------------------------------

Running 'Factorial design specification'

Failed  'Factorial design specification'

Error using spm_meanby (line 31)

row dimension mismatch between inputs

In file "/Users/andre/Documents/MATLAB/spm12/spm_meanby.m" (v1143), function "spm_meanby" at line 31.

In file "/Users/andre/Documents/MATLAB/spm12/config/spm_run_factorial_design.m" (v6219), function "spm_run_factorial_design" at line 623.

The following modules did not run:

Failed: Factorial design specification

Can anybody guide how the specify the batch for this.  

Thank you very much

André