AFNI Message Board

Dear AFNI users-

We are very pleased to announce that the new AFNI Message Board framework is up! Please join us at:

https://discuss.afni.nimh.nih.gov

Existing user accounts have been migrated, so returning users can login by requesting a password reset. New users can create accounts, as well, through a standard account creation process. Please note that these setup emails might initially go to spam folders (esp. for NIH users!), so please check those locations in the beginning.

The current Message Board discussion threads have been migrated to the new framework. The current Message Board will remain visible, but read-only, for a little while.

Sincerely, AFNI HQ

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bob cox
February 05, 2004 01:25PM
You will probably find that there is no collinearity in this baseline model. Even the r=1 case, f1(t)=cos(PI*(t-t0)/(tN-t0)) is not a linear function, which the -polort 1 default baseline creates.

However, although t and f1(t) are linearly independent, they are fairly similar. So it would make sense to use -polort 0 to have the builtin baseline model reduced to just a constant. This would reduce the chance of numerical problems from near-collinearity.

Have you tried this method with 3dDeconvolve yet? I'm curious to hear your results. If there is a problem, you could reduce the set to a smaller basis using some sort of PCA.

Also, you can use the little-known AFNI program 1deval to calculate these additional baseline time series.

Zorkon the Magniloquent

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Subject Author Posted

baseline model colinearity

giuseppe pagnoni February 05, 2004 12:26PM

Re: baseline model collinearity and highpass filtering

bob cox February 05, 2004 01:25PM

Re: baseline model collinearity and highpass filtering

giuseppe pagnoni February 05, 2004 02:37PM