Date: Nov 6, 2013 3:53 AM
Author: Tim
Subject: Re: one-way repeated measures ANOVA with more levels than subjects

OK, I have now heard back from the original author of the function. Though this is not stated in the code, the implementation is a MANOVA and not a repeated measures ANOVA.

I will now simply implement a repeated measures ANOVA for fieldtrip.

Thanks again for your help, your suggestions towards the MANOVA helped solving this riddle.
Tim


On Friday, October 25, 2013 5:18:01 PM UTC+2, tkie...@gmail.com wrote:
> On Thursday, October 24, 2013 1:27:38 AM UTC+2, Jeff Miller wrote:
>

> > On Thursday, October 24, 2013 10:37:52 AM UTC+13, Bruce Weaver wrote:
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> >
>
> > > For those who are interested, here's the code:
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> >
>
> > > http://code.google.com/p/fieldtrip/source/browse/trunk/statfun/statfun_depsamplesF.m?r=935
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> >
>
> >
>
> >
>
> > This part of the code looks suspect to me:
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> >
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> >
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> >
>
> > nunits = max(design(cfg.uvar,:));
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> >
>
> > dfdenom = nunits - ncontrasts;
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> >
>
> >
>
> >
>
> > I'm not confident, but it looks to me like:
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> >
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> >
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> >
>
> > nunits = the number of subjects.
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> >
>
> > ncontrasts = (at least by default) the number of df's
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> >
>
> > for the repeated measures factor factor.
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> >
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> >
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> >
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> > In that case, dfdenom for the factor effect in a repeated measures design should be (nunits-1)*ncontrasts.
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>
>
> Hi Jeff,
>
>
>
> Thanks for looking into this. The line you are referring to is the suspicious one (in fact the one that made me wonder whether I had a conceptual misunderstanding here).
>
>
>
> Below the line, they compute the actual F statistic with
>
>
>
> for smplindx=1:nsmpls
>
> datonesmpl=reshape(dat(smplindx,poslabelsperunit),nunits,nconds);
>
> contrasts=datonesmpl*cfg.contrastcoefs';
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> contrastavg=mean(contrasts,1);
>
> dev=contrasts-repmat(contrastavg,nunits,1);
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> covmat=(dev'*dev)/(nunits-1);
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> s.stat(smplindx)=nunits*contrastavg*inv(covmat)*contrastavg';
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> end;
>
>
>
> Apparently, they are comparing the factor levels to their average, which makes a MANOVA unlikely. I will go and see whether there is something on this in the fieldtrip mailing list. I will keep you updated.
>
>
>
> If someone has a suggestion in the meantime, of course please let me know about it.
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>
>
> Thanks again for your help and advice
>
> Tim