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I thought that I could not remove the class since this would mean that
the contrast positive and negative values would no longer add up to 0.
For instance if I remove only class "patient_centre2_female", then my
contrast would have 11 (-1) and 12 (1) as opposed to 12 and 12. Could
you please clarify?
Thanks again,
Colleen
-------- Original Message --------
Subject: Re: [Freesurfer] FSGD design for multi-centre study
Date: 2018-04-20 11:19
From: "C.P.E. Rollins" <cper2(a)cam.ac.uk>
To: Freesurfer <freesurfer(a)nmr.mgh.harvard.edu>
Thanks a lot for the explanation. The issue is that I don't think
Freesurfer will run a design for which there are no subjects for a given
class. So if I keep the classes (24 classes since 6 centres x 2 gender x
2 groups (patient vs. control), and have the contrast with 12 (-1) and
12 (1),
-1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 1 1 1 1 1 1 1 1 1 1 1 1 0
I get the error:
--------------------------------
ERROR: matrix is ill-conditioned or badly scaled, condno = 1e+08
--------------------------------
Possible problem with experimental design:
Check for duplicate entries and/or lack of range of
continuous variables within a class.
I'm assuming this is because there are no participants in, for example,
patient_centre2_female
Is there any way to get around this issue, or should I remove those
centres from my analysis (since I can't only remove
"patient_centre2_female", as this would make the contrast unbalanced
(positives and negatives would not add to the same number). I hope this
was clear but please let me know if it was not.
Thanks again,
Colleen