Calculations for comparing two estimated relative risks This calculator works off-line. (IE4)

Programme written by DJR Hutchon. Enter data into the boxes
Group 1
Relative risk
95% confidence interval from to
Group 2
Relative risk
95% confidence interval from to

Ratio of relative risk (RRR) = Test of interaction (z score)
95% confidence interval of RRR =
A permanent record of the analysis can be obtained by printing the page.
Ref: Douglas G Altman, J Martin Bland, Statistics Notes Interaction revisited: the difference between two estimates BMJ 2003;326:219 ( 25 January ) "The comparison of two estimated quantities, such as relative risks, each with its standard error. The two estimates should be independent, not obtained from the same individuals. Examples are the results from subgroups in a randomised trial or from two independent studies. The samples should be large."

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