[FieldTrip] montecarlo statistic inversion

[Jac Billington]

Dear experts,

I'd be grateful if someone could explain to me why there is an inversion in the statistics for the dependant sample montecarlo option - depending on the tail chosen

I'm running the code below- a 0 or -1 tail seems to result in the lowest stat.stat value having the most significant p. A tail of '1'  flips this relationship (and is more in line with my result if I run a stats anova1 option). I've also extracted all the electrode results and placed them in another software (SPSS) and these results reflect the anova1  / montecarlo tail of '1'. See dropbox link below.

Happy with suggested readings, but I really can't place why this may be the case, or the best option to choose.

Thank you. Jac


https://www.dropbox.com/s/liq79s2ppzqpht2/m_carlo_comp.jpg?dl=0

cfg = [];
cfg.channel = {'all'};
cfg.latency = time;
cfg.frequency = frq;
cfg.method = 'montecarlo' ; %%%%'stats' %
cfg.statistic = 'depsamplesFmultivariate' %%%%%'anova1';
cfg.correctm = 'no';
% cfg.clusteralpha = 0.05;
% cfg.clusterstatistic = 'maxsum';
% cfg.minnbchan = 2;
% prepare_neighbours determines what sensors may form clusters
cfg_neighb.method = 'distance';
cfg.neighbours = ft_prepare_neighbours(cfg_neighb, dataEEG);
cfg.tail = 0; %%% (-1 1)
cfg.clustertail = 0;
cfg.alpha = 0.05;
cfg.numrandomization = 5000;
cfg.avgoverchan = 'no'
cfg.avgovertime = 'yes'
cfg.avgoverfreq = 'yes'
subj = length(selsubs);
design = zeros(2,4*subj);
for i = 1:subj
design(1,i) = i;
end
for i = 1:subj
design(1,subj+i) = i;
end
for i = 1:subj
design(1,subj+subj+i) = i;
end
for i = 1:subj
design(1,subj+subj+subj+i) = i;
end

design(2,1:subj) = 1;
design(2,subj+1:2*subj) = 2;
design(2,subj+subj+1:3*subj) = 3;
design(2,subj+subj+subj+1:4*subj) = 4;
cfg.design = design
cfg.uvar = 1;
cfg.ivar = 2;

%%%%stats option
%cfg.design = design(2,:) %% stats option
%cfg.ivar = 1;

[stat] = ft_freqstatistics(cfg, frequencyR{1}{:}, frequencyR{2}{:},frequencyR{3}{:},frequencyR{4}{:})



Dr Jac Billington
Associate Professor - Perceptual Neuroscience
School of Psychology, Rm G.06A
University of Leeds
Leeds, LS2 9JT
Tel: +44(0)113 343 6686

|| Orcid Profile<https://orcid.org/0000-0003-0995-8875> || Twitter<https://twitter.com/billingtonjac?lang=en> ||


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https://doi.org/10.1371/journal.pcbi.1002202