Date: Tue, 2 Nov 2010 14:16:50 -0400
Reply-To: Jordan H <jihool3670@GMAIL.COM>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: Jordan H <jihool3670@GMAIL.COM>
Subject: huge (>999.99) odds ratios: cause?
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First, a little background. I've been asked to help with a project in which
the goal to develop a model that predicts high cost pharmacy expenditures
based on a variety of variables, such co-morbidities, demographics, etc. To
do this, a multivariate regression model was used. My client is also
interested in trying to model poor prediction within the multiple regression
model. To do this, they saved the residuals from PROC REG, made an
indicator variable for those observations with residuals greater than 1.75,
and ran a PROC LOGISTIC with the new indicator variable as the response
variable and the original independent variables, plus additional cost
variables, as predictors.
The model converges and most coefficients/odds ratios look reasonable but
some appear to be errors (odds ratios of >999.99, confidence intervals
(<0.001 - >999.99). We've checked things like multicollinearity but that
doesn't seem to be an issue.
Does anyone have an idea as to what could be going on?
Thank you for your consideration!