Dear FreeSurfer experts,

I am doing a repeated measures ANOVA 2x2 (2 groups and 2 time points) and I would like to include in the analysis a covariate that is constant over the 2 times (e.g., baseline medication).

I would like to see a "group x time x covariate" interaction.

What should the design look like? I know that without covariate the design is as follows:

GroupDescriptorFile 1
Class Subject1
Class Subject2
Variables                Tp1vsTp2.Group1   Tp1vsTp2.Grroup2
Input Subject1_time1 Subject1         1                                 0
Input Subject1_time2 Subject1        -1                                0
Input   Subject2_time1 Subject2         0                                 1
Input Subject2_time2 Subject02      0                                 -1

Design matrix:
1 0 1 0
1 0 -1 0
0 1 0 1
0 1 0 -1

Contrasts (.mtx files):
Tp1vsTp2.Group1 0 0 1 0
Tp1vsTp2.Group2 0 0 0 -1
Interaction (timexgroup) 0 0 1 -1

However, I do not know how I could include the interaction with that covariate.

Thank you very much in advance.

Kind regards,

Agurne