Dear all,
I am performing a statistical comparison of FA maps from two groups (patients and controls), with age and sex as covariates, after having done TBSS. I do not assume an interaction between age x group (neither sex x group).
I have strange results when changing the design matrices and the use of -D option.
I have done two analyses:
1) Design Matrix
Group EV1(Patients/Controls) Age Sex
1 -1 -22 -1
1 1 11 1
1 1 31 1
1 -1 -20 -1
Contrasts
1 0 0 (patients > controls)
-1 0 0 (controls > patients)
With these matrices, I ran the randomize with the -D option (as I read from the forums)
2) Design Matrix
Group EV1(Patients) EV2(Controls) Age Sex
1 0 1 -22 -1
1 1 0 11 1
2 1 0 31 1
2 0 1 -20 -1
Contrasts
1 -1 0 0 (patients > controls)
-1 1 0 0 (controls > patients)
And in this case, following some recommendations on the forum, I did not use the -D option.
I had very different results with these two designs, especially regarding the p values. What is the good design ? (if one of those is good ??)
Thanks,
Josselin Houenou
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