Dear FreeSurfer experts,
I am trying to use the LME toolbox to analyse the hippocampal change over time in a group and also among 2 groups (2 scans per subject).
When I estimate the parameters with lme_fit_FS I become a warning saying that the matrix is singular and my results are NaN. I guess that my design matrix X is not correct, can you please help me?
I have followed the example from the wiki. My model for the two groups study is the following:
Yij = ß1 + ß2*tij +ß3*Group1 + ß4*Group1 *tij + ß5*Group2 + ß6*Group2 *tij+ ß 7*Genderi + ß8*Agei + ß9*ICVi + b1i + b2i*tij + eij
1) intercept (all ones)
2) time (tij) . Here I have 0s for the first scan of each subject and a number in years for the second scans. Is it correct?
3) one for Group1 and zero otherwise
4) colum 3) .* time
5) one for Group2 and zero otherwise
6) colum 5) .* time
7) Gender
8) Age of the subject at each scan moment.
9) ICV (converted to liters).
Thank you in advance, Yolanda