```Date: Thu, 12 Aug 2010 08:22:37 -0700 Reply-To: haiyan chen Sender: "SAS(r) Discussion" From: haiyan chen Subject: Re: Calculating Incident Rates Comments: To: Billy Thompson In-Reply-To: <201008121415.o7CAki0F026106@willow.cc.uga.edu> Content-Type: text/plain; charset=iso-8859-1 you have a binomial distribution B(n=4, p=10%); your researcher is interested in p(x=2)={4!/(2!*2!)]*square(10%)*square(90%)=0.486. --- On Thu, 8/12/10, Billy Thompson wrote: From: Billy Thompson Subject: Calculating Incident Rates To: SAS-L@LISTSERV.UGA.EDU Date: Thursday, August 12, 2010, 10:15 AM I researcher approached me with the following question... We have 4 patients with an event.  2 of the patients have an abnormal MRI, 2 are normal.  The normal population incidence of MRI abnormalities is 10%. The question is what is the likelihood of 2 of 4 having the MRI abnormality, given the population likelihood of 10%, and what are the confidence intervals. Another colleague and I feel that CI's are not appropriate and that there are pieces of the puzzle missing, however I'm always open to suggestions and the opportunity to learn. Any help is greatly appreciated. ```

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