[FieldTrip] ft_freqstatistics and FDR-correction

[Patricia Wollstadt]

Dear Fieldtrip-users,

I'm currently trying to calculate freqstatistics for four experimental groups, using the following options:

groupSize=[length(subjects{1}) length(subjects{2}) length(subjects{3}) length(subjects{4})];

design = [1:groupSize(1)+groupSize(2)+groupSize(3)+groupSize(4)];            % 1 to N subjects
design(2,:) = [ones(1,groupSize(1)) 2*ones(1,groupSize(2)) 3*ones(1,groupSize(3)) 4*ones(1,groupSize(4))]; % indep var -> group membership


cfg=[];
cfg.design=design;
cfg.uvar = 1;       
cfg.ivar = 2;    
cfg.method = 'montecarlo';
cfg.statistic = 'indepsamplesF';
cfg.correctm = 'fdr';
cfg.numrandomization = 180000;
cfg.alpha = 0.01/7;
cfg.tail = 1;
cfg.design = design;
cfg.channels = myChannels;
cfg.avgovertime = 'yes';
cfg.avgoverfreq = 'yes';
cfg.frequency = [1 3];

stat = ft_freqstatistics(cfg, group1avg, group2avg, group3avg, group4avg);

With these settings, the coputation itself runs fine, but the resulting  'prob'-matrix contains only zeros (accordingly the 'mask'-matrix consists of only ones). This would mean, that I found significant effects for all channels. Is this possible or rather due to an error somewhere in my script? Is it likely, that these are 'real' zeroes or rather very small values, close to zero?
Any hints and suggestions are very welcome, thank you in advance,

Kind regards

Patricia Wollstadt


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