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

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 journa ls and conference proceedings, and by contacting researchers. Data were ext racted on the number of participants, quality of concealment of allocation, use of blinding, loss to follow up, and types of participants, interventio ns, 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 evide nce of increasing size over time. The total number of randomised participan ts in the 203 trials in which size was reported was 16 613. No trials were large enough to detect reliably a 5% absolute I-eduction in the risk of dea th or disability and only 4% were large enough to detect an absolute reduct ion 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 asses sing disability, 111 reported the number of patients followed up, and avera ge loss to follow up was 19%. Of trials measuring disability, 26 (21%) repo rted that outcome assessors were blinded. Conclusions Randomised trials in head injury are too small and poorly desig ned to detect or refute reliably moderate but clinically important benefits or hazards of treatment Limited funding for injury research and unfamiliar ity with issues of consent may have been important obstacles.