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Size and quality of randomised controlled trials in head injury: review of published studies

BMJ 2000; 320 doi: (Published 13 May 2000) Cite this as: BMJ 2000;320:1308
  1. Karen Dickinson, medical studenta,
  2. Frances Bunn, review group coordinatora,
  3. Reinhard Wentz, information specialista,
  4. Phil Edwards, research fellowa,
  5. Ian Roberts, director (ian.roberts{at}
  1. a Cochrane Injuries Group, Child Health Monitoring Unit, Department of Epidemiology and Public Health, Institute of Child Health, London WC1N 1EH
  2. b Child Health Monitoring Unit, Department of Epidemiology and Public Health, Institute of Child Health
  1. Correspondence to: I Roberts
  • Accepted 3 February 2000


Objective: To assess whether trials in head injury are large enough to avoid moderate random errors and designed to avoid moderate biases.

Design: All randomised controlled trials on the treatment and rehabilitation of patients with head injury published before December 1998 were surveyed. Trials were identified from electronic databases, by hand searching journals and conference proceedings, and by contacting researchers. Data were extracted on the number of participants, quality of concealment of allocation, use of blinding, loss to follow up, and types of participants, interventions, and outcome measures.

Results: 279 reports were identified, containing information on 208 separate trials. The average number of participants per trial was 82, with no evidence of increasing size over time. The total number of randomised participants in the 203 trials in which size was reported was 16 613. No trials were large enough to detect reliably a 5% absolute reduction in the risk of death or disability, and only 4% were large enough to detect an absolute reduction of 10%. Concealment of allocation was adequate in 22 and inadequate or unclear in 25 of the 47 (23%) in which it was reported. Of 126 trials assessing disability, 111 reported the number of patients followed up, and average loss to follow up was 19%. Of trials measuring disability, 26 (21%) reported that outcome assessors were blinded.

Conclusions: Randomised trials in head injury are too small and poorly designed to detect or refute reliably moderate but clinically important benefits or hazards of treatment. Limited funding for injury research and unfamiliarity with issues of consent may have been important obstacles.


  • Funding The Cochrane Injuries Group is funded by the NHS Executive.

  • Competing interests None declared.

  • Accepted 3 February 2000
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