Endgames Statistical Question

Randomised controlled trials: evaluating and communicating treatment effects

BMJ 2014; 348 doi: https://doi.org/10.1136/bmj.g1905 (Published 07 March 2014) Cite this as: BMJ 2014;348:g1905

This article has a correction. Please see:

  1. Philip Sedgwick, reader in medical statistics and medical education,
  2. Katherine Joekes, senior lecturer in clinical communication
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, London, UK
  1. p.sedgwick{at}sgul.ac.uk

Researchers investigated the efficacy of the anticoagulant fondaparinux in older acute medical inpatients at moderate to high risk of venous thromboembolism. A double blind randomised placebo controlled trial study design was used. The intervention was 2.5 mg fondaparinux subcutaneously once a day for six to 14 days. Participants were 849 acute medical patients aged 60 years or more who were admitted to hospital.1

The primary outcome was venous thromboembolism detected by routine bilateral venography. In total, 644 patients (75.9%) were available for the analysis of the primary outcome. Venous thromboembolism was detected in 5.6% (18/321) of patients treated with fondaparinux and 10.4% (34/323) of those given placebo. The reduction in risk of venous thromboembolism with fondaparinux compared with placebo represented an absolute risk reduction of 4.9% (95% confidence interval 0.7% to 9.2%) and relative risk reduction of 46.7% (7.7% to 69.3%). The number needed to treat was 20.4.

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

  • a) The absolute risk reduction of venous thromboembolism for fondaparinux compared with placebo was significant

  • b) The relative risk reduction of 46.7% of venous thromboembolism with fondaparinux compared with placebo represented a relative risk of 0.533

  • c) The number needed to treat estimates that, on average, for every 20.4 patients given fondaparinux one would not develop venous thromboembolism


Statements a and b are true, whereas c is false.

The aim of the trial was to investigate the efficacy of …

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