Once again, thank you for your answer Dr. Zalesky!

Just to clarify some things if I want to evaluate the linear increase: time1 < time2 < time3 and also taking into account that we have 2 groups (good performers vs. poor performers) then my design matrix for an example with 4 subjects will be something like this:

1 1 0 0 0 0 0 1 0 0 0 
1 0 2 0 0 0 0 1 0 0 0
1 0 0 4 0 0 0 1 0 0 0 
1 1 0 0 0 0 0 0 1 0 0
1 0 2 0 0 0 0 0 1 0 0
1 0 0 4 0 0 0 0 1 0 0
1 0 0 0 1 0 0 0 0 1 0
1 0 0 0 0 2 0 0 0 1 0
1 0 0 0 0 0 4 0 0 1 0
1 0 0 0 1 0 0 0 0 0 1
1 0 0 0 0 2 0 0 0 0 1
1 0 0 0 0 0 4 0 0 0 1

where columns 2 to 4 model time for group1 and columns 5 to 7 model time for group2. The last 4 columns model each subject.
The contrast for linear increase in the group 1 will be: [0 -1 0 1 0 ...] Is this contrast correct? Because you mentioned that contrasts will be [0 1 0 0...] for t1 > t2 > t3 and [0 -1 0 0...] for t1 < t2 < t3, but I don't get it how this reflects the linear increase.


Thanks in advance!
Best regards,
Ana