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st: question re simulation


From   "Lachenbruch, Peter" <lachenbruch@cber.fda.gov>
To   "'lebautista@wisc.edu'" <lebautista@wisc.edu>, "statalist (E-mail)" <statalist@hsphsun2.harvard.edu>
Subject   st: question re simulation
Date   Tue, 13 Apr 2004 13:42:06 -0400

The query was to find a 95% confidence interval of Y=A*B/K.  A simple method
would be to take logs giving
Log(Y)=log(A)+log(B)-log(K)
If these are independent then var(log(Y))=var(A)/A2+var(B)/B2 +var(K)/K2 but
K is constant so the last term drops out.  You can get a confidence interval
for log(Y) and then exponentiate the lower and upper limits.  Note that the
logs here are natural logarithms.

Peter A. Lachenbruch
Director, Division of Biostatistics, OBE/CBER
Tel: (301) 827-3320
FAX: (301) 827-5218

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