Hi
It is not necessary to make these corrections in order for your results to
be *valid*, but the reviewer is probably thinking that it would be
interesting to see regional changes that are "on top of" the global
effects. I don't really agree with the reviewer that this is *necessary*.
Cheers.
> Dear all,
> I have a (probably trivial) statistical question.
> We performed a study on a rare genetic illness and found differences both
> in VBM analyses (using SPM software and adjusting for TIV) and TBSS.
>
> The reviewer asked:
>
> "Global grey matter volume, white matter volume and CSF volumes should be
> reported (these can be extracted from the VBM pre-processing procedure).
> If significant case-control differences are identified these should be
> accounted for in regional analysis. ie VBM and TBSS analyses may need to
> be discussed with and without co-variation for global differences."
>
> I have no problem to calculate GM and WM volumes (probably CSF volume is
> more difficult, because often unreliable), but what is difficult to
> understand for me is why should I have to correct my statistics for global
> differences in GM/WM.
> I will appreciate any help or reference. Thank you!
>
> Angela
>
>
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