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st: RE: binary proportions and sample size


From   "Visintainer PhD, Paul" <Paul.VisintainerPhD@baystatehealth.org>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   st: RE: binary proportions and sample size
Date   Wed, 25 Mar 2009 17:57:21 -0400

Nicola,

You can't do a "statistical test", yet, because you haven't specified what your "expectation" (ie., null hypothesis) is.  What you can do is determine the degree of precision you have for your estimate, by computing the confidence interval.

.cii 74 4

This gives your estimate of the proportion of problem tools as 5.4% with a 95% confidence interval of 1.5% to 13.2%.  From a practical point of view, this means that if you were to review all 900 tools, the true proportion of problem tools is likely to fall somewhere between 1.5% and 13.2% (with 95% certainty).  If your sample of 74 was truly random, then 5.4% is a good guess of what you find in the population.




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