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Date:         Tue, 27 Jul 2010 16:02:18 -0400
Reply-To:     William Shakespeare <shakespeare_1040@HOTMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         William Shakespeare <shakespeare_1040@HOTMAIL.COM>
Subject:      Logistic regression predictors

Suppose I have a list of customers and their sales going back several years. The list is ever expanding since new customers are always being added and some customers are repeat purchasers.

Now suppose I have a hunch that a 2010 Q2 purchase can be predicted by Q2 purchases in previous years. I'm only interested in predicting whether or not someone bought, not the amount, so my outcome is binary while my predictors are continuous.

The question I have concerns the Q2 purchases in previous years. It's possible that person A could have multiple purchases, say 2005 Q2, 2008 Q2, and 2009 Q2 as well at the target quarter (2010 Q2). Do the repeated predictors represent a violation of the independence assumption if they contain the same subjects? Clearly if I were looking at repeated outcome measures it would, but here I have repeated predictors. Collinearity could also be a problem that's dealt with easily enough.

I seem to remember this question being posted a while back but I don't kow what the answer was and I can't find it.


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