I think that's ok. In the end you want the best models, you just need to
make sure that there is no significant group-by-parameters interaction. Not
intervening can also cause a bias. For example if there is atrophy in one
group that allows the surfaces to avoid dura but in the other group
significant dura is included you will overestimate effect sizes
cheers
Bruce
On Mon, 16 Feb 2015, Silas wrote:
Hi Bruce,
Thanks for your answer. My data quality isn't always as good as i could have
hoped. This unfortunately impairs freesurfers ability to distinguish between
grey matter surface, dura and skull. In specific cases I've found it
rewarding to change the parameters in order to gain a better fitting of the
pial surface to the actual grey matter surface. Afterwards I've made manual
editing to obtain the best possible fit. These parameter changes isn't group
specific. Would you still avoid changing the parameters?
Best, Silas
> Date: Mon, 16 Feb 2015 09:28:05 -0500
> From: fis...@nmr.mgh.harvard.edu
> To: freesurfer@nmr.mgh.harvard.edu
> Subject: Re: [Freesurfer] Changing wstresh and removing wsg-atlas -
consequences?
>
> Hi Silas
>
> you should certainly try to avoid a group-by-processing parameters bias.
> Is there a reason that one group would require different parameters than
> another?
>
> cheers
> Bruce
> On Mon, 16 Feb 2015, Silas wrote:
>
> > Hi Freesurfer team,
> > I'm currently making an structural analysis using freesurfer. In the
> > analysis i'm comparing 3 groups; 2 patient groups with different
reactions
> > to a certain type of medication and a healthy control group. In the
> > freesurfer pipeline i'm changing the parameters wsthresh and wsgatlas in
> > order to obtain a better fitted pial surface and white matter surface -
and
> > i was wondering if changing these parameters affect the comparability of
the
> > 3 groups (if e.g. i would like to investigate the inferior frontal
gyrus)?
> >
> > Best, Silas
> >
> >
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