Probably the easiest thing to do since you have only two time points is to compute the difference between the two, then just do a simple group analysis where you include the covariates that you want.

On 3/23/2022 10:00 AM, Agurne Sampedro Calvete wrote:

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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

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