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Dear Sir, Thank you very much for all the information, it is very useful On 11/23/10, Mark Jenkinson <[log in to unmask]> wrote: > 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] >> > -- Dr. BHAVANI SHANKARA BAGEPALLY MBBS, (PhD in Clinical Neuroscience) NIMHANS, Bangalore, INDIA-560029 email: [log in to unmask]