Endgames Statistical Question

Controlled trials: allocation concealment, random allocation, and blinding

BMJ 2015; 350 doi: https://doi.org/10.1136/bmj.h2633 (Published 15 May 2015) Cite this as: BMJ 2015;350:h2633
  1. Philip Sedgwick, reader in medical statistics and medical education
  1. 1Institute for Medical and Biomedical Education, St George’s, University of London, London, UK
  1. p.sedgwick{at}sgul.ac.uk

The efficacy of nicotine patches in pregnant women who smoke was investigated using a randomised placebo controlled trial. The intervention was the administration of 16 hour nicotine patches until the time of delivery. Participants were 402 pregnant women older than 18 years who smoked at least five cigarettes a day and whose babies were between 12 and 20 weeks’ gestation. Women were recruited from 23 maternity wards throughout France. To ensure allocation concealment, the allocation sequence was randomly generated by computer by someone independent of the trial. After recruitment, participants were allocated to intervention patches (n=203) or placebo patches (n=199) according to the allocation sequence.1

The primary outcome measures were achievement of complete abstinence until delivery and birth weight. The proportion of women who achieved complete abstinence was higher in the nicotine patch group than in the placebo group, although the difference was not significant (11 (5.5%) v 10 (5.1%); odds ratio 1.08, 95% confidence interval 0.45 to 2.60). The mean birth weight was higher in the nicotine patch group, although the difference was not significant (3065 g (standard error 44 g) v 3015 g (44 g); difference 50 g, −71.1 to 172.3). It was concluded that the nicotine patch did not increase smoking cessation rates or birth weights.

Which of the following statements, if any, are true?

  • a) Allocation concealment ensured that the allocation sequence was not known by women before recruitment to the trial

  • b) Allocation concealment reduced the …

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