In SAS EG 4.3, I'd like to run proc quantreg with effect command specified as natural cubic splines, something like proc quantreg data = one; effect spl_age = spline(age / naturalcubic knotmethod = list(3 6 9 11 14)); model outcome = spl_age; run; I kept on encountering error message telling me error with using "naturalcubic". What is the correct way to use natural cubic splines in effect command? Is this a SAS9.3 new feature? How do we do this if I am in older version SAS? Thank you.
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