title: Size and quality of randomised controlled trials in head injury: review of published studies.
abstract: OBJECTIVE
  To assess whether trials in head injury are large enough to avoid moderate random errors and designed to avoid moderate biases.
  
  
  METHODS
  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.
authors.affiliation: Cochrane Injuries Group, Child Health Monitoring Unit, Department of Epidemiology and Public Health, Institute of Child Health, London WC1N 1EH.
authors.forename: K
authors.initials: K
authors.lastname: Dickinson
authors.forename: F
authors.initials: F
authors.lastname: Bunn
authors.forename: R
authors.initials: R
authors.lastname: Wentz
authors.forename: P
authors.initials: P
authors.lastname: Edwards
authors.forename: I
authors.initials: I
authors.lastname: Roberts
mesh_terms: D015982:Bias; D006259:Craniocerebral Trauma / Q000628:therapy*; D006801:Humans; D016032:Randomized Controlled Trials as Topic / Q000592:standards*; D018401:Sample Size