Calculator for confidence intervals of relative risk This calculator works off-line. (IE4)

Programme written by DJR Hutchon. Enter data into the boxes "A","B","C",and "D"
Group characteristic
(A+C) (B+D)
OUTCOMETotal "better" A+B= A = B =
Total "no better" C+D C = D=

Relative risk R =
95% confidence interval = or treatment is
A permanent record of the analysis can be obtained by printing the page.
Ref: Gardner M J and Altman D G. Statisitics with confidence. BMJ publications. Reprint 1994 p 51-52
Relative risk = (A/{A+C})/(B/{B+D})
Standard Error oflog Relative risk(SElogR) =sqrt((1/A)-(1/(A+C))+(1/B)-(1/(B+D)))
lower limit= the exponential of (log(Rel risk)-(1.96*SElogR))
upper limit= the exponential of (log(Rel risk)+(1.96*SElogR))

This calculator is for educational use. It is believed accurate but no responsibility for accuracy of the results is accepted by the author. David J R Hutchon BSc, MB, ChB, FRCOG Consultant Gynaecologist, Memorial Hospital, Darlington, England.
You are welcome to keep this page and use the calculator off-line. I would appreciate an E-mail if you find it useful enough to do so. E-mail to me at

Last modified: 01/08/2010 16:46:34