Hello all,
This is actually an extension of a previous email:
http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind0104&L=spm&D=0&P=3769
I am looking at the paper:
Analysis of fMRI Time-Series Revisited-Again
and I have some questions.
I understand and accept that SPM uses the pseudoinverse when performing
the least sqaure analysis to avoid any singularites that
may arise due to multicollinearity in the design matrix. However on page 3
of the above manuscript are the equations for Var{b} and T which both
include:
(GT*G)-1*GT which is evaluated with the pseudoinverse. However
what about:
G*(GT*G)-1
which exist in both of these equations?
Is this inversion possible? If the psudoinverse is used to avoid
any multicollinearity issues how does this second equation get evaluated
if there is multicollinearity?
I hope that I am making some sense and not picking at a minor
point.
thank you,
Jason.
Jason Steffener, RTS V
Department of Psychiatry
New Jersey Medical School
Newark, NJ USA
(973) 972-1604
http://www.umdnj.edu/~steffejr
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