[FieldTrip] doublecheck significance cfg.alpha and cfg.clusteralpha

Meeren.H.K.M. hanneke.meeren at uvt.nl
Fri Jan 28 13:03:34 CET 2011

Dear Fieldtrippers,

I am relatively new to fieldtrip, and just starting to make some serious use of the cluster-based permutation routines, and I would just like to (double)check something before I continu.

I use ft_timelockstatistics with the following configuration structure:
cfg.parameter = 'individual';
cfg.method = 'montecarlo';
cfg.statistic = 'depsamplesT';
cfg.correctm = 'cluster';
cfg.clusteralpha = 0.05;
cfg.clusterstatistic = 'maxsum';
cfg.minnbchan = 2;
cfg.tail = 0;
cfg.clustertail = 0;
cfg.alpha = 0.025;

>From my understanding of the tutorial the "cfg.clusteralpha" stands for the alpha-value used for the initial test-statistic (in my case a paired t-test) for thresholding the data, and that the "cfg.alpha" field contains the alpha-value for the second step, i.e. selecting clusters after the permutation tests. 

However, the naming of the parameters seems rather contraintuitive to me. I would have expected it to be the other way around, i.e "cfg.clusteralpha" for my clusters (second step), and not the initial t-test.

Could anyone confirm (or deny) the way it is written in the tutorial?

Thanks a lot, 

Hanneke Meeren

Hanneke K.M. Meeren, PhD.
Researcher and Lecturer
Medical Psychology and Cognitive Neuroscience
Tilburg University
P.O. Box 90153
5000 LE Tilburg
The Netherlands
email: hanneke.meeren at uvt.nl

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