# [FieldTrip] Defining a custom statfun for cluster statistics

Lozano Soldevilla, D. (Diego) d.lozanosoldevilla at fcdonders.ru.nl
Mon Jun 2 10:01:15 CEST 2014

```Hi Stephen, You can take a look to ft_statfun_diff.m function: it's a good example to start with. You might also want to take a look here: http://fieldtrip.fcdonders.nl/faq/how_can_i_test_an_interaction_effect_using_cluster-based_permutation_tests Regarding the abs(ttest(Ia,Ib))-abs(ttest(IIa,IIb)), I'm not sure what the output of your statistic would mean. best, Diego ----- Original Message -----
> From: "Stephen Politzer-Ahles" <spa268 at nyu.edu>
> To: fieldtrip at donders.ru.nl
> Sent: Monday, 2 June, 2014 9:39:57 AM
> Subject: [FieldTrip] Defining a custom statfun for cluster statistics
> Hello all,
> Are there any examples for defining a new statfun to use in
> ft_timelockstatistics? I thought there were, but can't currently find
> them on the wiki.
> I am testing a 2x2 interaction (let's call the conditions Ia, Ib, IIa,
> and IIb), and I an only interested in a certain kind of interaction,
> one where abs(Ia-Ib) is large and abs(IIa-IIb) is small (i.e., an
> effect of the second factor at just one level of the first factor, and
> not the other level). So rather than using F as my test statistic for
> defining clusters, I would like to use something like
> abs(ttest(Ia,Ib))-abs(ttest(IIa,IIb)). I just don't know how to define
> the function to do this; if anyone could point me in the right
> direction I would greatly appreciate it.
> Thanks!
> Steve
> Stephen Politzer-Ahles
> New York University, Abu Dhabi
> Neuroscience of Language Lab
> http://www.nyu.edu/projects/politzer-ahles/
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-- PhD Student Neuronal Oscillations Group Donders Institute for Brain, Cognition and Behaviour Centre for Cognitive Neuroimaging Radboud University Nijmegen NL-6525 EN Nijmegen The Netherlands http://www.ru.nl/people/donders/lozano-soldevilla-d/
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