Dear Freesurfer experts,
I have three groups g0, g1, and g2.
I am trying to use LME model with random effects y-int and time from the base line.
Based on the LME tutorial and the questions and answers from Freesurfer support list:
Y=B1+B2*t+B3*g1+B4*g1*t+B5*g2+B6*g2*t+ …
The slope of g0 : 0 1 0 0 0 0 The slope of g1: 0 1 0 1 0 0 The slope of g2: 0 1 0 0 0 1
The slope difference between g0 and g1: 0 0 0 1 0 0 The slope difference between g0 and g2: 0 0 0 0 0 1 The slope difference between g1 and g2: 0 0 0 -1 0 1
1) Is this contrast matrix correct to observe pairwise slope difference?
In the tutorial the contrast matrix C = [zeros(3,3) [1 0 0 0 0; -1 0 1 0 0; 0 0 -1 0 1] zeros(3,6)]
2) Is it necessary to combine contrast matrix of the pair difference the same as the tutorial?
If so, my contrast matrix can be C=[0 0 0 1 0 0; 0 0 0 -1 0 1]
3) How can we interpret the result for this contrast matrix?
4) How can I obtain B1, B2, … ?
[sz1,sz2] = lme_plannedSampleSize(Zi,ZiCol,Dhat,phisqhat,effsz,... dr,pw,alpha,gr_pr)
5) For sample size calculation how can I get Dhat ( Estimated random effects covariance matrix) and phisqhat (Estimated intra-subject variability)?
With regards
Getaneh