Encyclopedia of Pain

2007 Edition

Attributable Effect and Number Needed to Treat

  • Nikolai Bogduk
Reference work entry
DOI: https://doi.org/10.1007/978-3-540-29805-2_318


Efficacy; effectiveness; number needed to treat; NTT


The  Attributable Effect of a treatment is the extent to which it achieves its outcomes, beyond that achieved by non-specific effects of the intervention. It is the extent to which outcomes can be attributed to the specific components of a treatment by which it is purported to work.

The  number needed to treat (NNT) is a measure of how effective a treatment is. Specifically, it is the number of patients who must achieve a particular outcome before one of those patients, on average, can be claimed to have responded because of the specific effects of the treatment (as opposed to having responded to the non-specific effects of treatment). As a measure of the power of a treatment, NNT effectively discounts the apparent power by the extent to which outcomes are achieved by non-specific effects. The larger the number, the more the treatment works by non-specific effects. The smaller the number, the more the treatment...

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Copyright information

© Springer-Verlag Berlin Heidelberg 2007

Authors and Affiliations

  • Nikolai Bogduk
    • 1
  1. 1.University of NewcastleDepartment of Clinical ResearchRoyal Newcastle HospitalNSW, Australia