Dear all
I'm trying to compare the cortical thickness between the neurodegenerative disease patient group and normal controls.
To match the age, I selected subjects from both groups and finally included age-matched groups into freesurfer thickness analysis (similar mean age, same age distribution from 40-73, 70 normal controls and 91 patients)
In 1st qdec analysis, direct comparison between two groups without age covariate showed thickness of temporoparietal cortex of patient group was smaller than that of normal controls (uncorrected P<0.001 or FDR corrected P<0.05).
However, when the age was included in the model as a covariate, the significant surface vertices almostly disappearred and some unexpected vertices emerged as significant, in which mean thickness were not so much different between two groups.
My question is...
1) Is there any possibility that disease-related cortical thinning area is quite similar to the age related cortical thinning area and resulted in the disappearance of significant vertices?
2) Do I have to include age covariate in that model even if I clearly matched the age distribution?
3) The area "does the average thickness differ between normal and patient?" was just same as the area "does the thickness--age correlation differ between normal and patient?", except for the color of blobs (e.g. red -> blue, blue -> red). Then, what do those question mean?
From Lyoo