On 11 July 2017 at 11:20, Katharina W.
<[log in to unmask]> wrote:
> Dear CAT12 experts,
>
> since we used the option "modulation for non-linear transformations only" in the VBM8 toolbox and it is now in CAT12 only available in the expert mode, I was looking for the reasons why it is not recommended anymore.
>
> The CAT12 manual refers to Malone et al. 2015.
>
> Are there more papers in this direction that point to more precise results using a modulation of all transformations and adjusting for TIV later on?
>
> Thank you in advance and best wishes,
> Katharina
Hi Katharina,
I wont claim to be a CAT12 expert, but I can explain some of the
thinking behind that. Essentially overall brain size and the sizes of
different structures are not (across populations) proportional to TIV,
so directly scaling by TIV can actually introduce a variation due to
TIV that wasn't there before, or overcorrect and simply change the
direction. On top of that you have noise from the TIV estimation that
you're introducing into the ratio.
How much it matters depends exactly what comparison you intend to do.
Are your groups significantly different in mean or variance of TIV (or
TIV correlated with your EV)? If yes, you may be introducing that
significant difference into the experiment. If not then less of a
problem, but still not the best way to deal with noise. I used to keep
some references on this area, it may not be completely up to date, but
here are a few:
Nordenskjöld 2015
http://www.sciencedirect.com/science/article/pii/S0925492714003084
doi:10.1016/j.pscychresns.2014.11.011
Pintzka 2015 http://journal.frontiersin.org/article/10.3389/fnins.2015.00238/abstract
doi:10.3389/fnins.2015.00238
Voevodskaya 2014
http://journal.frontiersin.org/article/10.3389/fnagi.2014.00264/abstract
doi:10.3389/fnagi.2014.00264
Hansen 2015 http://www.ajnr.org/content/early/2015/04/09/ajnr.A4299
doi:10.3174/ajnr.A4299
Liu 2014 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4222222/
doi:10.3389/fnins.2014.00356
And on the reliability of ratio measures:
Arndt 1991 http://www.sciencedirect.com/science/article/pii/092549279190031K
doi:10.1016/0925-4927(91)90031-K
--
imalone
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