[Eeglablist] Help with LIMO ANCOVA/Regression and STUDY cluster analysis

Dr Cyril, Pernet wamcyril at gmail.com
Tue Feb 2 03:04:29 PST 2021

Hi Deniz
> I have   a STUDY design with 2 independent groups, and each subject has a single EEG file that consists of 2 conditions recorded during the same session. So I have 2 factors for the variable group (between subject)  and 2 factors for the variable condition (within subject).
> So far with my Study design and using LIMO, I am able to run a repeated measure ANOVA with condition as the repeated variable and group as the between subject factor, and groupxcondition as the interaction term.
> My goal is to test the correlation between ERP components and the behavioral outcome of my task
> 1)ANCOVA-LIMO - I would like to explore the relationship between the main effects and a potential covariate.

the 'best' thing to do would be to compute contrasts, i.e. [1 -1 0] for 
each subject which is your main effect, then ANCOVA 2 gp and covariates

[...] What I tried was (after precomputing channel measures for ERPs, 
power spectrum and ERP-image):
> 1)First level analysis: Estimate model parameters (beta files), with interaction term, OLS, and selected timeframe.
--> no interaction - you do group statistics (anyway there should be any 
to compute given 2 conditions only ie your design should have 3 columns, 
if so no need to recompute)
> 2)Second level analysis:
> Choose channel file, and work folder
> Run ANCOVA—> Full scalp analysis —> How many independent group?—>enter 2—>Load beta or con files? —> load beta files for each group separately (gp1 and gp2)_—> Which parameters to test?—> Enter [1 2] for my repeated conditions (n=2) —> Here I see the error:

yes my bad -- there should a message preventing you to do that ; you 
cannot do rep. measures here (will include in the next patch)

as explained above, use contrasts from 1st level instead.

> 2)Regression-LIMO
> I also thought that if ANCOVA did not work, I could run a regression model separately for each independent group.
> In the tutorial it gives an example of creating a first level contrast for each subject, and then run a-sample t-test to create the con files which would be used in the regression model along with the regressor variable. I was wondering if there is a way to use parameters from the repeated measure ANOVA model as they would account for the noise better, or maybe it would not differ much since I used OLS?
well see above -- if you split the ANCOVA covariates (ie use 
XXXXXX000000 and 00000XXXXX with values) say for age, then you model 
separately the effect of age for each group - which allws you to test [1 
-1] if group differ, [0 0 1 -1] if the effect of age differ, [0 0 1 1] 
the common effect of age

Dr Cyril Pernet,
Centre for Clinical Brain Sciences (CCBS)
Neuroimaging Sciences

wamcyril at gmail.com

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