I usually use quadratic. I would not worry too much about trying to extract out every last drop of efficiency. Things are going to change enough when you actually analyze the data. What you want to do is just avoid having really bad sequences.

doug

Leo Fernandino wrote:

Hi there,

I noticed that when I include additional polynomials as nuisance variables, the efficiency of the design decreases. When should we include polynomials to account for scanner drift, and how do we decide the maximum order of the polynomials? Does it depend only on the length of the run? My runs are 8 min each, am I justified in having a quadratic polynomial?

Thank you,

Leo Fernandino

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Leonardo Fernandino, Ph.D. Post-Doctoral Scholar Human Neuroscience Laboratory Department of Neurology The University of Chicago 5841 S. Maryland Ave. MC-2030 Chicago, IL 60637 Phone: (773)-834-7847 http://www.fmri.uchicago.edu/

"Those who cannot remember the past are condemned to repeat it." - George Santayana

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