# 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.

Outcome | ||||
---|---|---|---|---|

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 |

## Calculations

### 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]}

## Example

## Variations

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

## References

- ↑
^{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]} - ↑ 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. - ↑
^{3.0}^{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]} - ↑
^{4.0}^{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]} - ↑
^{5.0}^{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]} - ↑ 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: