Intended for healthcare professionals

Endgames Statistical Question

Block randomisation

BMJ 2011; 343 doi: (Published 09 November 2011) Cite this as: BMJ 2011;343:d7139
  1. Philip Sedgwick, senior lecturer in medical statistics
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, Tooting, London, UK
  1. p.sedgwick{at}

Researchers evaluated the effectiveness of a newly developed integrated care programme to help patients with chronic low back pain return to work. The programme was a combined patient and workplace directed intervention, delivered in the outpatient setting. A randomised controlled study design was used, with usual care being the control treatment. The study period was one year.1

Trial participants were recruited from primary and secondary care if aged between 18 and 65 years and they had had low back pain for more than 12 weeks. In total 134 participants were allocated to the integrated care programme or to control treatment by block randomisation, with a block size of four. The researchers reported that the duration of time until a fully sustained return to work was significantly shorter for patients receiving integrated care than for those undergoing usual care.

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

  • a) Block randomisation ensured similar numbers of patients in the treatment groups.

  • b) Participants were randomly allocated four at a time, with all …

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