Hello everyone, I am trying to calculate predicted values for a fit from rq (quantreg; see my earlier post), but I am having trouble understanding how to interpret the coefficents in the summary.rq table generated by contr.poly. This probably applies equally to lm objects as well. I've checked in Crawley's and Dalgaard's extremely helpful books, where I found clear explanations of how to interpret the results of contr.treatment and the others. Can someone recommend a place to look for an equally simple explanation of contr.poly? Also, what is the advantage of using contr.poly over contr.treatment for ordered factors? Is it improper to use contr.treatment for ordered factors? Many thanks in advance, Sincerely, Matt R. Matthew Landis, Ph.D. Dept. Biology Middlebury College Middlebury VT 05753 tel. 802/443.3484 fax.802/443.2072 [[alternative HTML version deleted]]