Von: John Herrington <[log in to unmask]>
An: [log in to unmask]
Gesendet: Dienstag, den 22. September 2009, 16:22:57 Uhr
Betreff: [SPM] Using DCM modulatory effects as descriptive statistic for GLM
I have a question about whether a particular way of using output from DCM is
valid. In particular, I was wondering if it was valid to use the
"modulatory effects" values of a single DCM as descriptive statistics that
could be submitted to other statistical inference tests (particularly
GLM-based ones). Say, for example, that I have a single DCM model that
contains only two brain regions (A and B), and only one task condition
(i.e., no condition-specific effects are being examined for present
purposes). The DCM is
set up to allow for both bi-directional intrinsic and
modulatory effects between A and B. I want to ask a simple question - does
activity from A modulate B, or vice versa. The null hypothesis would be
that there's no difference between the modulatory effects of A and B on one
another. Could I treat the modulatory effect values of A-to-B and B-to-A as
descriptive statistics and submit them to a t-test to see if they differ? I
realize that this could be handled using the DCM comparisons approach (i.e.,
examinations of AIC/BIC) of two unidirectional models, but there seem to me
to be some advantages to using a null hypothesis test approach as above, it
it's feasible.
Thanks,
John