Hello list,
what model would be suitable to investigate if a genetical polymorphism
with three levels is associated with altered grey matter volume?
Usually in VBM t-tests / two-group ANCOVAs are used.
In SPM5 would this be a one-factor, three-level analysis (plus three covariates)?
What would the F-contrast be that asks if there is a significant association between
the genetical status and GM volume?
(regardless of the direction of the effect (i. e. more or less GM)?)
With the polymorphisms encoded in the first three colums I used an F-contrast
1 0 0 ...
0 1 0 ...
0 0 1 ...
and find very strong effects. However, I am not sure if this contrast makes sense.
The pairwise t-contrasts (A<B, B<A, A<C, C<A, B<C, C<B) calculated from the same model
also reveal effects which seem very weak as compared with the F-contrast above.
thanks a lot for any help here,
Philipp
|