Hi Jill Tao, Thanks for your prompt reply. What about smoothing spline (the SSPLINE option)? When I use "model identity(Y)=smooth(X/xm=20)", smoothing spline transformation is done in (x,y) pairs and no tX produced. If I use "model identity(y)=sspline(x/xm=20)", however, a tX is present in the output dataset. How is this tX from SSPLINE derived? SAS documentation also mentions smoothing spline transformation uses penalty function similar to PSLINE. The problem is PSLINE has a list of different penalty functions to choose from. Which specific penalty function is used by SMOOTH or SSPLINE in SAS Transreg? Thanks again, Lana
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