Freqstatistics Yields Zero Significant Clusters?

[Erick Britis Ortiz]

Dear Eric,

this is the configuration used for the analysis.

% Configuration for statistics
cfg = [];
cfg.channel     = 'MEG';
cfg.latency     = [ 0.0 0.6 ];
cfg.avgovertime = 'no';
cfg.method      = 'montecarlo';
cfg.numrandomization = 1000;
cfg.statistic   = 'depsamplesT';
cfg.alpha       = 0.05;
cfg.tail        = 0;
cfg.correctm = 'cluster'; cfg.grad = grad;
cfg.clusteralpha = 0.05;
cfg.clusterstatistic = 'maxsum';
cfg.minnbchan = 2;
cfg.clustertail = 0;
cfg.design(1,1:2*numsubj)  = [ones(1,numsubj) 2*ones(1,numsubj)];
cfg.design(2,1:2*numsubj)  = [1:numsubj 1:numsubj];
cfg.ivar                = 1; % the 1st row in cfg.design contains the
independent variable
cfg.uvar                = 2; % the 2nd row in cfg.design contains the
subject number

Cordially,
Erick


Eric Maris wrote:
> Dear Erick,
>
>
>> Following up on the discussion, we have also tried to use the cluster
>> option for multiple comparisons correction in a previous study and
>> thought that our results were not significant. Now, we tried again with
>> 1000 randomizations and cfg.correctm = 'cluster', to no avail. Since we
>> are interested in p<0.05, 1000 iterations seem large enough, but most of
>> the probabilities calculated are near or equal to 100%. Further testing
>> with 10000 permutations yielded similar results.
>>
>> We are fairly sure that there is something there, because calculating
>> analytically we see big clusters that extend in a consistent way to
>> neighboring frequency and time bins, even at low p thresholds (<10^-4).
>> Since Bonferroni is over-strict, Montecarlo is the option of choice for
>> a corrected result that we will trust. But now something seems off.
>
>
> Can you post the configuration that you used for these analyses?
>
>
> dr. Eric Maris
> Donders Institute for Brain, Cognition and Behavior
> Center for Cognition and F.C. Donders Center for Cognitive Neuroimaging
> Radboud University
> P.O. Box 9104
> 6500 HE Nijmegen
> The Netherlands
> T:+31 24 3612651
> F:+31 24 3616066
> E: e.maris at donders.ru.nl
>
> MSc Cognitive Neuroscience: www.ru.nl/master/cns/

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