Hello.
I agree that this is an important issue that needs more discussion.
I have often thought that a degrees of freedom map could be used. So
instead of assuming you have a fixed dof across the brain one would
have dof that vary. This of course complicates interpretation but
results could be reported based on height of significance for all
voxels with dof greater than some value. And as research studies are
starting to use larger and larger number of subjects, I feel this
approach is starting to become more viable.
Now how this would affect cluster extents and thresholds is another issue.
This approach is possible, but only with some coding.
Jason
On Sat, Mar 17, 2012 at 8:47 AM, Elizabeth Liddle
<[log in to unmask]> wrote:
> When a study involves a large number of participants, the cumulative effect
> of a few voxels masked out in each subject at 2nd level analysis can lead to
> a very small group mask, even though for any one voxel only a small number
> of subjects may have missing data. To make matters worse, often missing
> voxels are towards the edge of the image, meaning that the result composite
> mask is lacking the regions of greatest interest – the cortex near the
> skull.
>
>
>
> One solution, obviously, is to use an explicit mask, and another is to
> over-ride the default threshold of .8 for voxel inclusion at first level,
> but these solutions means that voxels that are, by definition, noisy, will
> be included. Do people on the list have any solutions to this problem?
>
>
>
> Elizabeth
>
>
>
> _____________________________________________________________________________
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> Dr Elizabeth Liddle
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> Lecturer in Translational Mental Health
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> Division of Psychiatry
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> Queen’s Medical Centre
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> University of Nottingham
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> NG11 2UH
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