Dear people familiar with GLM flex,
I am new to the GLM flex scripts (since yesterday), and so far everything worked great!
My goal is to be able to specify the correct error term manually.
Doing it manually is advised on the web-page (quoting from http://nmr.mgh.harvard.edu/harvardagingbrain/People/AaronSchultz/GLM_Flex_Intro_.html):
"The Cons.ET field allows you to specify which error term to use, if you leave that blank [], the scripts will attempt to choose the correct error term for you, but I cannot guarantee that the scripts will guess correctly, so it is best practice to specify this yourself."
However, I've not found any further information on what to base my judgment on, and in my case I have 4 error terms (ResMS_02%d.nii-files) to choose from!
(My design includes 1 between factor, 2 within, each having 2 levels).
In particular, I want to look at a single specific "column/level" of an interaction term.
I shall give a simpler example to explain what I mean:
Let's assume a design with two 2-level factors A and B, modeling both main effects (2 columns each) and its interaction (4 columns).
What is the full contrast specification to inspect the AxB-interaction's level A1,B1?
In particular, how can I determine the appropriate error term (field ET)?
In GLM-flex parlance, assuming main effects sitting at columns 1,2 and 3,4 this is what I would do:
I.Cons(1).name = 'A1,B1';
I.Cons(1).Groups = {5}; % the entire interaction columns span 5,6,7,8
I.Cons(1).Levs = 1;
I.Cons(1).ET = []; %TODO: gain understanding, and then filling it in manually!
I.Cons(1).mean = 0;
Any help, both practical and theoretical, is very much appreciated!
Johannes Keyser
Institute of Cognitive Science
University of Osnabrueck
