[FieldTrip] statistical reporting cluster based permutation

[Kaelasha Tyler]

Thanks Steve,

Very clear.
K.

PhD Candidate
Brain and Psychological Sciences Research Centre
Swinburne University of Technology
Melbourne
Australia
________________________________
From: fieldtrip-bounces at science.ru.nl [fieldtrip-bounces at science.ru.nl] on behalf of Stephen Politzer-Ahles [stephen.politzer-ahles at ling-phil.ox.ac.uk]
Sent: Sunday, 15 November 2015 10:15 PM
To: fieldtrip at science.ru.nl
Subject: Re: [FieldTrip] statistical reporting cluster based permutation

Hello Kaelasha,

There isn't really any one absolute right way to report these; my best suggestion is to look in the literature for other papers in your area that have reported cluster based stats, and see how they do it. In my experience it's usually sufficient to report the p-value, polarity, and approximate spatiotemporal distribution of an effect (e.g., "there was a significant positive effect (p=.042) based on a cluster of fronto-central electrodes lasting from x ms to y ms..."), as is done in this paper: https://www.researchgate.net/publication/38112722_Reasoning_with_Exceptions_An_Event-related_Brain_Potentials_Study.
I also find raster plots to be a nice way to visualize the spatiotemporal extent of a cluster; see, e.g., this paper: http://joshuakhartshorne.org/papers/HartshorneSnedekerLiemAzarKim.pdf

See also http://www.fieldtriptoolbox.org/faq/how_not_to_interpret_results_from_a_cluster-based_permutation_test for some suggestions about wording and interpretation of the effects.

Best,
Steve



---
Stephen Politzer-Ahles
University of Oxford
Language and Brain Lab, Faculty of Linguistics, Phonetics & Philology
http://users.ox.ac.uk/~cpgl0080/
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Date: Sun, 15 Nov 2015 01:07:30 +0000
From: Kaelasha Tyler <ktyler at swin.edu.au<mailto:ktyler at swin.edu.au>>
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Subject: [FieldTrip] statistical reporting cluster based permutation
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Hi all,

I am writing up results for cluster based permutation tests that I ran on masked priming meg data.

I have to admit I am not entirely sure the exact form for reporting the stats on these.

For example, when comparing two conditions, with n=20,  I have one significant positive cluster over left frontal and parietal areas. The stats for this cluster read:

prob: 0.0420
clusterstat: 1.2443e+04
stddev: 0.0063
cirange: 0.0124

Has anyone else completed and rerooted on results, having used cluster based permutation tests?
Mean values don't seem to be appropriate here, so would it simply be the p value and standard deviation for the significant clusters that would be reported on?

Thanks,
K

PhD Candidate
Brain and Psychological Sciences Research Centre
Swinburne University of Technology
Melbourne
Australia



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