[FieldTrip] assessing significance in using ft_timelockanalysis results

[Kanal Eliezer]

Hello Eric -

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!

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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