[Mne_analysis] group dSPM?

[Hari Bharadwaj]

Hi Elena,
  If you are using a fixed orientation solution, then the dSPMs are z
scores and can be combined in group studies using t-stats etc..

If you are using a free orientation solution, then depending on how you
combine the compnents you end up with an F or a chi2.. Atleast as a first
pass, you could compute group stats using a transform such as that goes
from chi2 (with 3 dof) to Z such as:
   y = (x/3)^(1/3)
y is then approximately distributed normally with mean (1 - 2/27)and
variance (2/27)

See: Wilson, E.B.; Hilferty, M.M. (1931) "The distribution of
chi-squared". Proceedings of the National Academy of Sciences, Washington,
17, 684–688.


We have usually dSPM scores non-parametrically (i.e using permutation type
tests) at the group level which might be the cleanest way of doing it but
very slow.
See: http://www.ncbi.nlm.nih.gov/pubmed/11747097


Regards,
Hari




On Fri, June 8, 2012 10:22 am, Alexandre Gramfort wrote:
> Hello Elena,
>
> there is one way that would consist is keeping track on the noise
> normalization
> used for each subject dSPM, then morph the noise normalization values too
> and then do the maths to average MNE estimates and divide by the mean
> noise normalization.
>
> Unfortunately there is build in way to do this currently...
>
> Alex
>
> On Fri, Jun 8, 2012 at 11:55 AM, Elena Orekhova
> <Elena.Orekhova at neuro.gu.se> wrote:
>> Dear MNE community,
>>
>>
>>
>> I would like to estimate reliability of the MNE activations on a group
>> level.  dSPM, that give us F values, can be performed in a single
>> subjects,
>> but what is about GROUP dSPM?
>>
>>
>>
>> I have seen the presentation by Daniel Goldenholz, where he speculates
>> on
>> possibility of the ‘group dSPM’ and I have seen the post by Marina
>> Papoutsi
>> (from February 18, 2009), where she tried to implement this analysis.
>> However, there was no news on this topic since then.  Does anybody use
>> the
>> ‘group dSPM’ and/or has any practical hints on that?
>>
>>
>>
>> Elena
>>
>>
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-- 
Hari Bharadwaj
PhD Candidate, Biomedical Engineering,
Boston University
677 Beacon St.,
Boston, MA 02215

Martinos Center for Biomedical Imaging,
Massachusetts General Hospital
149 Thirteenth Street,
Charlestown, MA 02129

hari at nmr.mgh.harvard.edu
Ph: 734-883-5954