```Date: Tue, 31 Oct 2006 01:00:08 -0800 Reply-To: Albert-jan Roskam Sender: "SAS(r) Discussion" From: Albert-jan Roskam Subject: Re: OR >999.999 Comments: To: Johanna LEPEULE In-Reply-To: <6.0.0.22.0.20061031083638.01b39570@sun.vet-nantes.fr> Content-Type: text/plain; charset=iso-8859-1 Hi Johanna, The OR expresses the odds that an event occurs divided by (--> ratio) the odds that this event does not occur. If the odds are very high, for instance the odds of people having two legs, your OR also becomes very high. Let's say this likelihood is 0.999. OR = p(have two legs) / p(have not two legs) = OR = 0.999 / (1 - 0.999) = 999. The phenomenon you're investigating is way too common to meet the so-called rare disease assumption. A rule of thumb is that the prevalence should be <10% for the OR to be a good estimate of the relative risk. Mr Bayes proved that long time ago. HTH, Albert-Jan --- Johanna LEPEULE wrote: > Hi > > I use a logistic model with one variable and I > obtain an OR and > 95%IC >999.999 without error message. > Does anyone have suggestions ? > > Thanks > Johanna Lepeule > > > ****************************************************** > Ce message a ete verifie par le systeme anti-virus > de l'Ecole Nationale Veterinaire de NANTES > > ****************************************************** > ____________________________________________________________________________________ Everyone is raving about the all-new Yahoo! Mail (http://advision.webevents.yahoo.com/mailbeta/) ```

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