[FieldTrip] ft_freqstatistics and FDR-correction

[Patricia Wollstadt]

Hi Rodolphe,

usually I compute this statistic for seven individual frequency bands (I left this part of the script out to keep the example-code short), so I did an additional correction of my alpha niveau. 

Regards,
Patricia


-------- Original-Nachricht --------
> Datum: Mon, 24 Jan 2011 11:39:31 -0600
> Von: Rodolphe Nenert <batrod at gmail.com>
> An: Email discussion list for the FieldTrip project <fieldtrip at donders.ru.nl>
> Betreff: Re: [FieldTrip] ft_freqstatistics and FDR-correction

> Dear Patricia,
> 
> Your alpha seems a little bit low, why taking 0.01/7= 0.0014 ?
> I may be wrong but i guess that a fdr correction on a such value of alpha
> will be very hard with your data.
> 
> Rodolphe N., PhD.
> 
> On Mon, Jan 24, 2011 at 10:47 AM, Patricia Wollstadt <
> Patricia.Wollstadt at gmx.de> wrote:
> 
> > 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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> >

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