[FieldTrip] Question about Dr Eric Maris et al. paper
Roemer van der Meij
r.vandermeij at donders.ru.nl
Sun Jan 9 12:49:05 CET 2011
After computing your cluster-level statistics you indeed take the
largest one, and this will be compared to the permutation distribution.
However, this distribution is constructed by doing the following e.g.
1) randomly swapping the units of observation (UO) between conditions
(in case of a between UO design)
2) computing your cluster-level-statistic for this random combination of UOs
3) taking the largest of these (largest of /all clusters/ in this random
permutation, not a /'selected' cluster/)
This will result in 500 'largest cluster-level-statistics'. If your
original statistic is bigger/smaller than a certain percentage, say 95%
when testing single-sided to an alpha of 0.05, then you reject the
null-hypothesis of interchangeability of your conditions. Whether it
should be bigger or smaller depends on your direction of testing.
Hope this helps,
On 9-1-2011 3:03, ?? ?? wrote:
> Dear Dr Eric Maris and members of Fieldtrip mailing list
> At first, I'm sorry for my poor English.
> I'm a post-doc research fellow of Department of Neuropsychiatry,
> Kyushu University, Fukuoka, Japan.
> I'm studying about auditory abnormalities in mental disorders, for
> example, schizophrenia, bipolar disorder, using MEG.
> I'm very impressed and interested in Dr Eric Maris and Dr Robert
> Oostenveld paper, "Nonparametrical statistical testing of EEG and MEG
> data, on Journal of Neuroscience Methods, 2007".
> I'd like to apply their stastical methods to our data, but there are
> some points that I can't understand in their paper.
> Those are about cluster-based statistics.
> In the right column in page 180 in their paper, they wrote 5 steps of
> statistics methods. At 5th step, they take the largest of the
> cluster-level statistics, then how do they test this largest of the
> cluster-level statistics?
> I thought that, after 5th step, I should make the permutation
> distribution of cluster-level statistics of selected cluster, and I
> should test the given cluster-level statistics with this permutation
> distribution. Is this right?
> Any answer will help me.
> Best regards,
> Shogo Hirano, M.D., Ph.D.
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
Roemer van der Meij M.Sc.
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognition
P.O. Box 9104
6500 HE Nijmegen
Tel: +31(0)24 3655932
E-mail: r.vandermeij at donders.ru.nl
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