Web Calculator for use with article on risk. This calculator works off-line.

Expressing the magnitude of risk of adverse effects in case-control studies:"the number of patients needed to be treated for one additional patient to be harmed" Reference: Lise M Bjerre, Jacques LeLorier BMJ 2000;320:503-506

Odds ratio = 95%confidence from to ( Use periods not commas for decimal points)
Duration of the follow-up of the case control study = years months
It is necessary to provide an unexposed event rate for the adverse event from another congruous source, either a randomised controlled trial or from unexposed subjects in cohort studies.
Unexposed event rate: number of adverse events = per subjects or patients
Over time interval = years months


Approximate 95% confidence interval from to
This CI is narrower than the true CI because it does not take into account the variability surrounding the unexposed event rate.
Glossary
NNTH=number of patients needed to be treated for one additional patient to be harmed
NNTB=number of patients needed be treated for one patient to be actually protected against the adverse outcome"
OR = ODDS RATIO = (odds of outcome event v odds of no event) in intervention group
(odds of outcome event v odds of no event) in conrol group

UER=unexposed event rate
CI = Confidence interval
Programme written by DJR Hutchon (copyright)
Go to A whole range of statistical calculators Go to NNT(B) & NNT(H) for controlled trial
Go to My home page

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.
Comments and suggestions are welcome and will be included in the comments section. E-mail to me at DJRHutchon@Postmaster.co.uk
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Last modified: 04/23/2015 00:52:28