Intended for healthcare professionals

Endgames Statistical Question

Randomised controlled trials with full factorial designs

BMJ 2012; 345 doi: (Published 01 August 2012) Cite this as: BMJ 2012;345:e5114
  1. Philip Sedgwick, reader in medical statistics and medical education
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, Tooting, London, UK
  1. p.sedgwick{at}

Researchers explored the effectiveness of three interventions in preventing falls among older people. The three interventions were group based exercise, home hazard management, and vision improvement. A randomised controlled trial with a full factorial design was used. The control treatment was no intervention. The study design allowed the effectiveness of each intervention to be evaluated plus exploration of their effects when combined. The researchers recruited 442 participants aged 70 years and over living at home in an urban community in Melbourne, Australia. The main outcome measure was self reported time to first fall after randomisation.1

The researchers reported that group based exercise was the most effective single intervention in reducing the number of falls. Falls were further reduced by the addition of home hazard management or vision management, or both.

How many treatment groups were there in the above randomised controlled trial that incorporated a full factorial design?

  • a) Four

  • b) Six

  • c) …

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