[Eeglablist] comparing normal and clinical populations

[Cyril Pernet]

Hi José,

Subject:
[Eeglablist] comparing normal and clinical populations
From:
Jose Rebola <jrebola at gmail.com>
Date:
04/12/2011 19:02

To:
eeglablist at sccn.ucsd.edu


 >Hi
 >I am running a study to investigate differences between  williams 
syndrome patients and controls in a visual task. I have eight subjects 
of each >population.
 >How do I compare the amplitude of the P100 between the populations?
 >Should i include only one value (the peak around 100ms on each of the 
subject's average) per subject ?
 >It seems to me that if i do this i will only have one value per 
subject and i am "throwing away" the 100 trials per condition that i have
 >Isn't there a way that i can compare between populations while 
retaining within-subject variability?


This is indeed a very valid point, if you only compute the average and 
take 1 value you do not account for within subject variance.
We have a toolbox LIMO_EEG which is fully compatible with EEGLAB and 
does hierarchical linear modeling, thus accounting for within and 
between subject variance - this handles pretty much any kind of design 
you may have. For a simple group comparison, you model the activity in 
your visual task for each subject (assuming either at least 2 conditions 
or 1 condition with some covariate like luminance, contrast, phase, etc) 
and then compare the parameters obtained between groups - at this stage 
LIMO_EEG use robust statistics making your inference much stronger.

You can access and download the toolbox @ 
https://gforge.dcn.ed.ac.uk/gf/project/limo_eeg/


 > Otherwise, how does it compensate to perform 1000 trials instead of 10?

mathematically speaking it is the same (in terms of variance) but of 
cource the average with 10 trials will be a poor representation of the 
neural activity.


Cyril


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