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Hi,
we have been struggling with the fitted and adjusted response
for PET data. Both from literature and the archives I understood
that the GLM could be written as:
Y = [X1:X2][beta1:beta2] + error
with [X1:X2] the design matrix split into effects
of interest and confounding effects
and [beta1:beta2] the corresponding model parameters.
giving for the adjusted and fitted response:
Y(adjusted) = Y - X2*beta2
= X1*beta1 + error
Y(fitted) = X1*beta1
So for a PET data set with conditions only, I expect the fitted
response to equal the betas for each condition. However, this is
not what I see in the figure or when I examine the data in the
Matlab workspace (SPM99).
So obviously, I am missing something. I just can't figure out what.
Any insight is appreciated,
Antoon Willemsen
Groningen University Hospital
The Netherlands
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