# [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

Hi Shogo,

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.
500 times:
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,

Best,
Roemer

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.
>
>
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> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip

--
Roemer van der Meij M.Sc.
PhD student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognition
P.O. Box 9104
6500 HE Nijmegen
The Netherlands
Tel: +31(0)24 3655932
E-mail: r.vandermeij at donders.ru.nl
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