Dear FreeSurfer experts,
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
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