Hi,
Raw _tstat_ images are indeed voxelwise - however I suspect that you
are looking at _tfce_tstat_ images, which look at spatial extent, so
will change if you change your mask.
Does this make sense? You could still find that your corrp
(corrected p-values) are improved through a more restricted mask fed
into randomise.
Cheers.
On 19 Aug 2009, at 19:58, Kirlic, Namik wrote:
> Hi,
>
> We have recently figured out how to use a mask to restrict the area
> of the
> skeleton evaluated in a DTI tbss group contrast of FA maps using
> randomise. It was our hope that the lesser number of comparisons would
> mean that the correction being done in the corrected p maps accurately
> reflects us taking in less territory. It had been our understanding
> that
> in a voxel-wise contrast, t values should not be affected by changing
> which voxels were evaluated, only p values. However, when we used the
> masks, our resulting t values were reduced overall, which leads us to
> believe that voxels are not evaluated independent of one another. Is
> this
> the case, and if so, does this mean that we cannot use a bonferroni
> type
> of correction ourselves based on the voxels we wish to consider?
>
> Thank you!
>
>
>
>
>
>
>
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