All you just need is NNT http://www.thennt.com  – the blog that puts “evidence based medicine under the microscope”.

With a clear explanation of what Number Needed to Treat actually means (it’s a “a measurement of the impact of a medicine or therapy by estimating the number of patients that need to be treated in order to have an impact on one person” BTW), and regular updates of evidence on different therapeutic interventions, NNT is a great site to help you get to grips with this calculation.

Other useful calculators are available at:

• Medcalc 
• – for Odds Ratio, and Relative Risk:   www.medcalc.org/calc/odds_ratio.php 
• UBC Clinical Significance Calculator 
• – for absolute risk reduction, relative risk reduction, odds ratio and NNT http://spph.ubc.ca/sites/healthcare/files/calc/clinsig.html

• Centre for Evicence Based Medicine 
• for more explanations of NNT, likelihood, and other critical appraisal tools http://www.cebm.net/index.aspx?o=1157