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Date:         Sat, 26 May 2007 13:17:54 -0700
Reply-To:     "Dennis G. Fisher, Ph.D." <dfisher@CSULB.EDU>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "Dennis G. Fisher, Ph.D." <dfisher@CSULB.EDU>
Subject:      Re: logistic regression wierdness
Comments: To: Peter Flom <peterflomconsulting@mindspring.com>
In-Reply-To:  <23813195.1180207896293.JavaMail.root@mswamui-blood.atl.sa.earthlink.net>
Content-Type: text/plain; charset=UTF-8; format=flowed

Peter, MV is ever use of both Methamphetamine and Viagra. The data actually make sense. The question is what to do about it? Thanks. Dennis

Peter Flom wrote: > Hi Dennis > > well, unless I am reading this wrong (it got formatted oddly) you only have 2 people in one of the cells....so, things are going to be weird! One could say that ANY model is overfit, because a single noise variable will suffice to put 1 person in the right cell > > What is MV? > > Peter > > -----Original Message----- > >> From: "Dennis G. Fisher, Ph.D." <dfisher@CSULB.EDU> >> Sent: May 26, 2007 1:58 PM >> To: SAS-L@LISTSERV.UGA.EDU >> Subject: logistic regression wierdness >> >> We are trying to construct a logistic regression model. When we put >> ever use of marijuana in the model, we get an odds ratio of 5.414 and >> the model seems to fit. We still get another 10 variables that seem to >> be OK. Usually when this kind of thing happens, I figure it is either >> dirty data or we coded something wrong, but this time I think it is >> real. The 2 x 2 table is >> Marijuana >> No Yes >> >> MV No 194 443 >> >> Yes 2 165 >> >> This is almost seems like a a quasi complete separation, but it really >> is not I don't think. I am going to feel really strange trying to >> present a model with an OR this big, but I cannot figure out why I >> should take it out of the model. What would you do? Thanks. >> >> Dennis Fisher, Ph.D. >> Center for Behavioral Research and Services >> California State University, Long Beach >> > > >


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