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From |
Ronan Conroy <rconroy@rcsi.ie> |

To |
statalist@hsphsun2.harvard.edu |

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

Date |
Thu, 2 Aug 2007 10:11:23 +0100 |

On 1 Aug 2007, at 13:55, Svend Juul wrote:

NNT = 15.230769 (95% CI: 5.0701399; -15.169883) - the negative numbers meaning that exposure to x may prevent low birthweight.

The negative number has the interpretation of Number Needed to Harm (with its minus sign removed), just as a negative Attributable fraction is more usually written as "Prevented fraction in the exposed/population"

Thus the confidence interval in Svend's example runs from an NNT of 5 to an NNH of 15.

The other useful statistic that I recommend is the NTN (number treated needlessly). It is the NNT-1. So if you have to treat 400 people to prevent one event, then the number treated needlessly is 399. A salutary reflection for the average doctor.

P Before printing, think about the environment

=================================

Ronan Conroy

rconroy@rcsi.ie

Royal College of Surgeons in Ireland

120 St Stephen's Green, Dublin 2, Ireland

+353 (0)1 402 2431

+353 (0)87 799 97 95

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**Follow-Ups**:**Re: st: Number Needed to be Treated (NNT)***From:*Richard Goldstein <richgold@ix.netcom.com>

**Re: st: Number Needed to be Treated (NNT)***From:*"Anders Alexandersson" <andersalex@gmail.com>

**st: Binomial regression***From:*Constantine Daskalakis <C_Daskalakis@mail.jci.tju.edu>

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

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