Number needed to treat

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The number needed to treat (NNT) is a way of summarizing the benefit of an intervention to improve health care.[1][2] The NNT has been proposed to improve quantitative literacy.[1] The calculations are derived from the results of a randomized controlled trial of an intervention.

Two-by-two table for a screening program
Present Absent
Experimental (intervention) group Cell A Cell B Total in experimental group
Control group Cell C Cell D Total in control group
Total with outcome Total without outcome


Event rates

Measures of efficacy

Deriving the NNT from the odds or risk ratios

The odds ratio may be used to derive the number needed to treat:[3][4]

For odds ratios less than 1:[4]

For odds ratios greater than 1:[4]

The relative risk ratio may be used to derive the number needed to treat:[3][5]

The relative risk reduction may be used to derive the number needed to treat:[3][5]



Years-needed-to-treat to add 1 year of life is proposed to estimate treatment effects.[6]


  1. 1.0 1.1 Laupacis A, Sackett DL, Roberts RS (1988). "An assessment of clinically useful measures of the consequences of treatment". N. Engl. J. Med. 318 (26): 1728–33. PMID 3374545[e]
  2. Wen L, Badgett R, Cornell J (2005). "Number needed to treat: a descriptor for weighing therapeutic options". Am J Health Syst Pharm 62 (19): 2031–6. DOI:10.2146/ajhp040558. PMID 16174840. Research Blogging.
  3. 3.0 3.1 3.2 Furukawa TA, Guyatt GH, Griffith LE (February 2002). "Can we individualize the 'number needed to treat'? An empirical study of summary effect measures in meta-analyses". Int J Epidemiol 31 (1): 72–6. PMID 11914297[e]
  4. 4.0 4.1 4.2 McQuay HJ, Moore RA (May 1997). "Using numerical results from systematic reviews in clinical practice". Ann. Intern. Med. 126 (9): 712–20. PMID 9139558[e]
  5. 5.0 5.1 Chatellier G, Zapletal E, Lemaitre D, Menard J, Degoulet P (February 1996). "The number needed to treat: a clinically useful nomogram in its proper context". BMJ 312 (7028): 426–9. PMID 8601116. PMC 2350093[e]
  6. Levy WC, Mozaffarian D, Linker DT, et al. (March 2009). "Years-needed-to-treat to add 1 year of life: a new metric to estimate treatment effects in randomized trials". Eur. J. Heart Fail. 11 (3): 256–63. DOI:10.1093/eurjhf/hfn048. PMID 19164422. Research Blogging.

See also

External links

Tables of NNTs for various treatments: