Intended for healthcare professionals

Endgames Statistical Question

Number needed to harm

BMJ 2011; 342 doi: (Published 11 May 2011) Cite this as: BMJ 2011;342:d2811
  1. Philip Sedgwick, senior lecturer in medical statistics
  1. 1Section of Medical and Healthcare Education, St George’s, University of London, Tooting, London, UK
  1. p.sedgwick{at}

Last week’s question described a trial that assessed the efficacy and safety of varenicline, a smoking cessation aid for users of smokeless tobacco.1 A double blind, placebo controlled, randomised controlled trial was performed. In total, 213 participants were allocated to varenicline and 218 to placebo. Treatment was for 12 weeks, with 14 weeks of follow-up after treatment.2

The primary end point was continuous abstinence from smoking for four weeks at the end of treatment (weeks 9 to 12). Secondary end points included adverse events. One of the most common adverse events was …

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