Freqstatistics Yields Zero Significant Clusters?
Erick Britis Ortiz
Erick.Ortiz at MED.UNI-TUEBINGEN.DE
Mon Jun 8 15:05:48 CEST 2009
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
cfg.uvar = 2; % the 2nd row in cfg.design contains the
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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