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From |
"Anders Alexandersson" <andersalex@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Number Needed to be Treated (NNT) |

Date |
Thu, 2 Aug 2007 16:20:05 -0400 |

Svend Juul and then Nick Cox wrote a small program to calculate number needed to be treated (NNT) based on -cs- and this was one example output: > NNT = 15.230769 (95% CI: 5.0701399; -15.169883) NNT is also related to the probability that variable for first group is larger than for second group, P(X>Y). For a reference, see Acion, L. et al. 2006. "Probabilistic index: an intuitive non-parametric approach to measuring the size of treatment effects". Statistics in Medicine 25(4): 591-602. There was a follow-up with reply later on pages 3944-3948. It seems to me that NNT = -(1/(2P(X>Y)-1)). Therefore, you can also calculate NNT quickly using either -ranksum- with the porder option or Roger Newson's command -somersd- with the tr(c) option: . ranksum low, by(x) porder- [output ommitted] . di -(1/((2*0.467)-1)) 15.151515 or, more precise and automated: . somersd x low, tr(c) . di -(1/((2*(1-_b[low]))-1)) 15.230769 This does not give a 95% confidence interval (yet) but is another way of calculating NNT. Anders Alexandersson andersalex@gmail.com * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**RE: st: Number Needed to be Treated (NNT)***From:*"Newson, Roger B" <r.newson@imperial.ac.uk>

**References**:**Re: st: Number Needed to be Treated (NNT)***From:*"Svend Juul" <SJ@SOCI.AU.DK>

**Re: st: Number Needed to be Treated (NNT)***From:*Ronan Conroy <rconroy@rcsi.ie>

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