Calculator for assessment of surgical success according to expects results This calculator works off-line. (IE4)

This calculator can be used to determine whether the 95% confidence intervals of the success rate achieved by a treatment regime (surgical or otherwise) includes the expected or publishedsuccess rate.

Enter numbers into the table for each time period. In "failures" and "censored" include those which have "failed" or been lost to followup in the relevant interval even if treated in a previous interval.
Expected success rate=%
YearNumber treatedNumber censoredNumber failedSuccess rate %Cumulative rate %95% confid int %
1( to )
2( to )
3( to )
4( to )
5( to )

A permanent record of the analysis can be obtained by printing the page.
For example a surgical team, following appropriate training, introduces a new or modified procedure. There are recognised complication rates and success rates from use of the procedure in other centres. The first case is complicated and is not a success. The complication rate so far is therefore 100% and the success rate is 0%. Should the team stop or consider retraining. While it is obviously good practice to review the case carefully, the calculator shows that the confidence intervals includes 0% success and therefore this does not suggest any system failure. This is common sense. However if after a further 9 cases 4 more have failed and there would be expected to be a 95% success rate, the calculator shows that this is just outside the range and clearly the "learning curve" may be operating.

Programme written by DJR Hutchon.

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

Martin J Gardner and Douglas G Altman Statistics with confidence BMJ 1989 Ch 7