Thanks Peter. I am trying to do this for a homework so I really am constrained in terms of choice of approach. I looked at the paper and I don't think it mentions how to use the F- value to stop the regression process. For instance, there is a part where it mentions the available stop criteria and there does not seem to be any mention of using F. I just want to be able to say, if F=4, remove/enter data. I'd like to know if SAS can do this. Thanks a lot for your time and for responding.