Dear FreeSurfer experts,
I would appreciate a confirmation regarding correctness of my approach.
I am trying to run an LME model for three groups (group1=controls, group2 and group3) and two time points.
I followed the tutorial on https://surfer.nmr.mgh.harvard.edu/fswiki/LinearMixedEffectsModels https://surfer.nmr.mgh.harvard.edu/fswiki/LinearMixedEffectsModels and adapted the four group example. However, I am not 100% sure if my adaption is correct and would appreciate your input.
The design matrix for the model contains the following columns:
1) Intercept
2) time (tij)
3) one for Group2 and zero otherwise
4) column 3) .* time
5) one for Group3 and zero otherwise
6) column 5) .* time
To test the null hypothesis of no group differences in the rate of change over time among the three groups I applied the following contrast:
0 0 0 1 0 0
0 0 0 -1 0 1
Is this contrast correct?
In a second step, I would use the additional three contrasts to identify which groups were different:
0 0 0 1 0 0 and 0 0 0 0 0 1 and 0 0 0 -1 0 0 1
I really appreciate your help!
Best wishes
Sarah