Hey freesurfers,

I'm interested in running an interaction between a continuous and categorical variable, covarying for another categorical variable. I understand that this analysis is not possible through the QDEC GUI so I am working through the command line group analysis and setting up the contrast matrix.

Discrete Factors:
Group with 2 levels: Patient and Control
Gender with 2 levels: Male and Female

Continuous variables:
Age

Meaning, I have 8 Regressors:
1: PatientMale intercept
2: PatientFemale intercept
3. ControlMale intercept
4. ControlFemale intercept
5: PatientMale age
6: PatientFemale age
7. ControlMale age
8. ControlFemale age

In order to look at the interaction of group and age, covarying for gender, would the matrix be:

0 0 0 0 -.5 .5 -.5 .5

However, this matrix seems looks more like a difference in slopes comparison and less like an interaction. Any help would be much appreciated!

Thanks,
Katie