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Vol. 14 - Num. 56

Critical appraisal in small doses

Calculating risk reduction and number needed to treat

Manuel Molina Ariasa

aServicio de Gastroenterología. Hospital Infantil Universitario La Paz. Madrid. España.

Correspondence: M Molina. E-mail:

Reference of this article: Molina Arias M. Calculating risk reduction and number needed to treat. Rev Pediatr Aten Primaria. 2012;14:369-72.

Published in Internet: 12-12-2012 - Visits: 30701


Although most scientific works usually analyze their data in terms of statistical significance, it is less frequent to find information about its clinical relevance. Calculating relative risks, relative risk reduction, absolute risk reduction and number needed to treat may help us to determine the clinical significance of the study results. Absolute risk reduction (risk difference between intervention and control branches) and its inverse value, number needed to treat, are the most useful figures to quantify the effort that will have to be made to achieve one more event of the desired effect.


Absolute risk reduction Number needed to treat Relative risk reduction Risk ratio



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