Sarah Cox <saslearner2006@GMAIL.COM>
>We are doing a decease trasfusion transmission study and found for total 34
>patients, no one is infeced. So the infection rate is 0. Right now, I need
>to calcluate the 95% CIs for the infection rate. Can any expert let me know
>how to calculate it because it is not a normal distribution? Your advice is
See Agresti and Coull "Approximate is better than exact for binomial confidence intervals" (that's the approximate title, anyway - it was in American Statistician a while back).
They have one complex formula to use (see the paper) or a simple quick and dirty one that works well, usually, which is to add 2 successes and 2 failures and then estimate. So, instead of 0/24, estimate the CI for 2/26.
But see the paper, and even do a google scholar search on papers that cited it. This area is full of counterintuitive findings (like larger N can be worse than smaller N).
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