FreeSurfers,
I have been analyzing my qdec data in version 5.0
and have some interesting although somewhat confusing results. Basically
I have run a very simple analysis with DODS and DOSS. My discrete
factor is group and my covariate is age, about as simple as can be.
When I look at the results for DODS I get:
thickness-age correlation (accounting for group)---result: much of brain significant
group difference (I assume controlling for age, but it doesn't say explicitly)--result: one small roi significant
thickness-age correlation group difference--result: one small roi spatially adjacent to group difference roi
When I run DOSS I get:
thickness-age correlation (accounting for group)---result: much of brain significant
group difference (I assume controlling for age, but it doesn't say explicitly)--result: much of brain significant
thickness-age correlation group difference--result: much of brain significant
I
am mostly surprised by how much larger the (group difference), and the
(thickness-age correlation group difference) increase with the DOSS
method. I am also not quite how to interpret the thickness-age
correlation group difference in DOSS. I was thinking the DOSS method
constrained both groups to have the "same slope" and so I was expecting
to get nothing for difference in thickness-age correlation difference by
group; isn't this suggesting my two groups have significantly different
ageXthickness slopes even though they are constrained to have the same
slope by the DOSS method? It would almost make more sense to me if the
results were reversed between DOSS and DODS. If I had a large
thicknessXage correlation group difference using the DODS method which
allows for different slopes. Thanks for any enlightenment.
Chris Bell
University of Minnesota