[FieldTrip] ft_freqstatistics and FDR-correction

[Rodolphe Nenert]

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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