[FieldTrip] Calculation of within-subject interaction

[Maren Grigutsch]

Dear Mariella,

in my opinion, both approaches are equivalent because

(A11 - A12) - (A21 - A22) = (A11 - A21) - (A12 - A22).

Best,
--Maren

On 08/16/2017 10:53 AM, mapaul at uni-osnabrueck.de wrote:
> Dear fieldtrip community,
>
> I found this very helpful tutorial on how to calculate an interaction
> effect using a cluster-based permutation:
>
> http://www.fieldtriptoolbox.org/faq/how_can_i_test_an_interaction_effect_using_cluster-based_permutation_tests
>
> I have a question regarding this step:
>
> Copy GA11 to GAdiff11_12 and perform the assignment
> GAdiff11_12.avg=GA11.avg-GA12.avg.
> Copy GA21 to GAdiff21_22 and perform the assignment
> GAdiff21_22.avg=GA21.avg-GA22.avg.
>
> I have a full within-subjects design and I was wondering if it matters
> which of my factors I define as factor 1 and which as factor 2. In other
> words, is there a difference between calculating
>
> GA11.avg - GA12.avg followed by GA21.avg - GA22.avg
> as opposed to GA11.avg - GA21.avg followed by GA12.avg - GA22.avg
>
> and then running a permutation test on the differences?
>
> Any help would be greatly appreciated!
>
> Thanks and with best regards,
> Mariella
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> https://mailman.science.ru.nl/mailman/listinfo/fieldtrip


-- 
Maren Grigutsch	

Max Planck Institute for Human Cognitive and Brain Sciences
Stephanstr.1a, 04103 Leipzig, Germany

Phone: +49 341 - 9940 136
Fax:   +49 341 - 9940 2260	
web:   www.cbs.mpg.de