Hi,
Unfortunately we don't have any other correction method implemented
currently, although we are working on them. I cannot really comment on
the biological implications of any of this, and caution you not to over-interpret
anything as a non-significant result does *not* imply that there was nothing
happening (or that it was intrinsically weaker) - it could be that, or it could just
be that the specific noise you had manifest as differences in sensitivity that
were like this, without any connection to biology. This is especially true if
one result is just over and another just under the statistical threshold. There
is normally no interpretation that can be made from such a result. If you are
interested in laterality differences then you need to formulate a statistical
test that directly looks for this and does not compare two different statistical
results, as that is itself not a statistically valid approach.
All the best,
Mark
On 22 Nov 2010, at 15:53, Bhavani shankara wrote:
> Thanks for the reply,
>
> is their any other method through which i can try other correction method (like FWE) to check the result. But on FDR uncorrected maps both hippocampus are showing difference between the groups.
>
> Is it may be due to biological reason of differential involvement in the structure of hippocampus between dominant and non-dominant hemispheres ??
>
> On Mon, Nov 22, 2010 at 9:16 PM, Mark Jenkinson <[log in to unmask]> wrote:
> Hi,
>
> This is perfectly reasonable for a couple of reasons:
>
> 1 - the volume change is not very spatially specific (or consistent)
> and hence you can have a strong overall volume change
> without a local vertex change (that is above threshold).
>
> 2 - the FDR thresholding is not the most sensitive technique for
> surface inference (we are working on coding up better ones)
> and so it is possible that it is just not quite sensitive enough
> although you might see interesting results in the uncorrected
> analyses. Unfortunately, the FDR results are very dependent
> on the small p-values which can be significantly influenced by
> slight outliers. It is worth looking at the uncorrected results to
> see if there is some consistent change which is just failing to
> meet the FDR threshold.
>
>
> I hope this helps.
> All the best,
> Mark
>
>
>
>
>
>
> On 22 Nov 2010, at 04:58, Bhavani shankara wrote:
>
> > Dear FSL experts,
> >
> > I am using FSL-FIRST, on extracting the Volumes and statistics were done on R software and found the subcortical structures and also both left and right hippocampus were significantly differing between the groups (AD and controls (all are right handed) ) (p<0.01).
> >
> > However on vertex analysis only on left side hippocampus is not differing between the groups standing out at FDR correction (on using surface_fdr input.vtk). However other structures including the sub-cortical deep gray matter regions were differing at FDR threshold output (p value) below 0.05.
> >
> > Is it possible ?? is it due to technical/analysis issue or due to biological reason??
> >
> > Thanks in advance for your response
> >
> > --
> > Dr. BHAVANI SHANKARA BAGEPALLY
> > MBBS, (PhD in Clinical Neuroscience) NIMHANS,
> > Bangalore,
> > INDIA-560029
> > email: [log in to unmask]
> >
>
>
>
> --
> Dr. BHAVANI SHANKARA BAGEPALLY
> MBBS, (PhD in Clinical Neuroscience) NIMHANS,
> Bangalore,
> INDIA-560029
> email: [log in to unmask]
>
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