Hi,
I have asked the question earlier but have not gotten a response. I'm
trying to use DCM for an fMRI study and have a question related to the
design matrix prior to DCM analysis.
I created a design matrix (attached) with 7 regressors (i.e.,
conditions) and an implicit baseline. The 1st regressor shares common
input with regressor 2-5, and will be used for the "input drive" to the
intrinsic connections. (Regressors 6-7 will not be included in the DCM
analysis.)
Questions:
1. As I understand, it's ok to have a non-orthogonal design matrix for
DCM analysis. Is that correct?
2. The design matrix indicates regressors 1-5 are "not uniquely
specified" and, therefore I can't define contrasts in "Results." I have
tried the "attention" dataset provided at the SPM Web site
(http://www.fil.ion.ucl.ac.uk/spm/data/). Its design matrix is
non-orthogonal, either. However, there is no warning on regressors "not
uniquely specified." And it allows t contrasts in Results. What's wrong
with my design? Will it affect the DCM analysis?
Any help is greatly appreciated.
Ben
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