[amelia] splinetime vs polytime options?

Hi Amelia users, The reason I was hitting the website was to see if there was any better documentation on the difference between the splinetime and polytime options in Amelia. My old code uses splinetime, and I have a comment saying "use splinetime, not polytime", but I forget exactly why and it isn't well documented in the PDF: ## polytime integer between 0 and 3 indicating what power of polynomial should be included in the imputation model to account for the effects of time. A setting of 0 would indicate constant levels, 1 would indicate linear time effects, 2 would indicate squared effects, and 3 would indicate cubic time effects. ## splinetime interger (sic) value of 0 or greater to control cubic smoothing splines of time. Values between 0 and 3 create a simple polynomial of time (identical to the polytime argument). Values k greater than 3 create a spline with an additional k-3 knot-points To me that says splinetime is a superset of polytime (values k in (0,1,2,3) are the same as polytime=k), which in turn implies to me that polytime is there only for backwards compatibility. Is that correct? Regards, James -- James E. Marca, PhD Researcher Institute of Transportation Studies AIRB Suite 4000 University of California Irvine, CA 92697-3600