Intended for healthcare professionals

Endgames Statistical Question

Number needed to treat II

BMJ 2011; 342 doi: (Published 04 May 2011) Cite this as: BMJ 2011;342:d2664
  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}

Researchers assessed the efficacy and safety of varenicline, a smoking cessation aid for users of smokeless tobacco. 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.1

The primary end point was continuous abstinence from smoking for four weeks at the end of treatment (weeks 9 to 12). Continuous abstinence was achieved by 59% of participants in the varenicline group and 39% in the placebo group, an absolute risk difference of 0.2. The relative risk of continuous abstinence between weeks 9 and 12 for varenicline compared with placebo was 1.60 (95% confidence interval 1.32 to 1.87; P<0.001).

Which one of …

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