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
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