[FieldTrip] assessing significance in using ft_timelockanalysis results

[Eric Maris]

Hi Elli,



> Thanks for the response. It looks like the fixed vs random analysis is
exactly
> what I'm referring to. From what I understood, it looks like the
difference
> really only shows up in the variance of the resultant distribution; with a
> random, the variance also takes into account the betwee-subjects variance.
> Is there a way to specify whether I want to do a fixed or random effects
> analysis in FieldTrip when I'm running ft_timelockgrandaverage or
> ft_freqgrandaverage? Thanks!


I don't get this. Ft_timelockgrandaverage and ft_freqgrandaverage will only
be called when a random effects analysis is performed.


Best,

Eric


> 
> Elli
> 
> p.s. - In case anyone else is trying to figure this out, chapter 12 of
Friston's
> book "Statistical Parametric Mapping" does an excellent job explaining the
> difference between fixed and random analyses, as well as how to implement
> it algorithmically.
> 
> 
> 
> On Aug 26, 2011, at 3:00 PM, Eric Maris wrote:
> 
> > Hi Kanal,
> >
> >> The event related statistics tutorial
> >> (http://fieldtrip.fcdonders.nl/tutorial/eventrelatedstatistics) talks
> > about
> >> assessing significance parametrically by running t-tests on pooled
> >> timelockanalysis data. My question is, does the fact that the averages
> > were
> >> created from N trials make a difference? If I'm condition A has twelve
> >> averages and condition B has another twelve, and each average contains
> 70
> >> trials, is there a way to "inform" the statistical test that the power
in
> > this
> >> dataset is greater than 24? Is this only possible if I run the t-test
> > comparing
> >> each set of 840 (70*12) trials?
> >>
> >> I'm also curious whether this is possible with non-parametric analyses,
as
> >> well. Thanks -
> >
> > In an analysis over subjects (called random-effects analysis in the fMRI
> > literature), "informing" the statistical test about the number of trials
per
> > condition only makes sense if this number is different for the two
> > conditions. I propose that you have a look the fMRI papers that deal
with
> > the issue of fixed-versus-random effect analyses. The conceptual issues
> > involved are the same in fMRI and electrophysiology.
> >
> >
> > Best,
> >
> > Eric Maris
> >
> >
> >
> >
> >>
> >> Elli Kanal
> >>
> >>
> >> --------------------
> >> Eliezer Kanal, Ph.D.
> >> Postdoctoral Fellow
> >> Center for the Neural Basis of Cognition
> >> Carnegie Mellon University
> >> 4400 Fifth Ave, Suite 110A
> >> Pittsburgh PA 15213
> >> P: 412-268-4115
> >> F: 412-268-5060
> >>
> >>
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> 
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