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Lars and David, 

Thank you for your thoughtful replies.  I find myself having to admit that if I ever truely understood linear regression back in the day it seems to have evaporated.  I am at the point now in all of this where I have to review a bit of math, lay out exactly what I'm trying to accomplish, and how best to learn about all the factors in an rigorous, controlled setting.  I think this is kind of what Ed was getting at.  I suspect, if I spend the time to look back in the archives I'll find such a discussion. 

I just want to say how much I appreciate the expertise and willingness to help the occasional straggler who wanders in to this amazing site.  If I haven't actually thanked you for a reply in the past it was because I didn't want to clutter up the thread.  But I learn a tremendous amount from this multi-faceted and talented group. 

Jim