[FieldTrip] interaction within-subject indepsamplesT

[Kathrin Müsch]

Dear Eric,

Thank you very much for your answer. I was afraid that this was the case.

Best,
Kathrin

Am 15.09.2011 um 10:10 schrieb Eric Maris:

> Dear Kathrin,
> 
>> I need your advice on how to correctly test the interaction effects in a
> 2x2
>> within-subject design with cluster-based randomization tests. I have two
>> factors A and B with the levels a1/a2 and b1/b2. In addition, the number
> of
>> trials in A are about twice as much as in B.
>> 
>> The procedure would be totally clear in a between-subject design (as in a
>> previous post on the list:
>> http://mailman.science.ru.nl/pipermail/fieldtrip/2011-January/003447.html)
> 
> This post is about a WITHIN-subjects design.
> 
>> because I could easily compute the differences of the factor levels
>> A_diff=a1-a2 and B_diff=b1-b2 and then run ft_freqstatistics on the
>> differences. However, since I have to run the statistics across trials and
> not
>> subjects I have independent samples and not dependent samples. 
> 
> So, you have a between-trials design.
> 
> If it is
>> possible at all, how can I calculate the differences A_diff and B_diff
> across
>> trials? Is it a problem that the number of trials are not equal?
> 
> This is not possible. Permutation tests cannot be used for testing
> interactions in a multi-factorial between-subjects/trials design. Michael
> Wibral has a post in which he refers to a nice statistics paper on the
> issue.
> 
> A proxy that is possible (but not statistically sound) is to perform two
> statistical tests of the first factor, once at the first level of second
> factor and once at the second level.
> 
> 
> Best,
> 
> Eric Maris
> 
> 
> 
> 
> 
> 
> 
> 
>> 
>> Any help is appreciated!
>> 
>> Best,
>> Kathrin
>> 
>> _____________________________________
>> Kathrin Müsch
>> 
>> Dept. of Neurophysiology and Pathophysiology
>> University Medical Center Hamburg-Eppendorf
>> Martinistr. 52
>> 20246 Hamburg
>> Germany
>> Phone: +49-40-7410-54680
>> Fax: +49-40-7410-57752
>> E-Mail: k.muesch at uke.uni-hamburg.de
>> _____________________________________
>> 
>> 
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> Alexander
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Pflichtangaben gemäß Gesetz über elektronische Handelsregister und Genossenschaftsregister sowie das Unternehmensregister (EHUG):

Universitätsklinikum Hamburg-Eppendorf; Körperschaft des öffentlichen Rechts; Gerichtsstand: Hamburg

Vorstandsmitglieder: Prof. Dr. Jörg F. Debatin (Vorsitzender), Dr. Alexander Kirstein, Joachim Prölß, Prof. Dr. Dr. Uwe Koch-Gromus