Hi Warren, Thanks a lot for your reply. I did try that (in addition to the original variables), and the model ended up selecting one of the two manually created basis. So I finally ended up creating an indicator variable instead with a value of 1 after the knot and a value of 0 before the knot, and using this indicator as a class variable. It isn't quite what I was looking for, but it is better than not having this knot in. Thanks again, Yves 2017
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