Traumatic injury to the CNS is a leading cause of death and acquired disability worldwide. It is estimated that well over 10 million people experience head injuries each year,1 of whom several thousand will die, and several thousand will be permanently disabled. The identification of effective strategies in the prevention, treatment, and rehabilitation of injury of the CNS is of considerable public health importance. Because the validity of effectiveness information from randomised controlled trials is far more readily assured than with other study designs, the randomised controlled trial has become the gold standard for evaluating treatment effectiveness. Many healthcare interventions have only moderate effects on outcome. However, for a problem as common as traumatic brain injury, even moderate effects can have important public health implications. Moderate treatment effects, whether favourable or adverse, are difficult to assess reliably, and require large amounts of randomised evidence. This evidence can be obtained in two ways: by conducting large scale prospective randomised trials, and by systematic review and meta-analysis of the evidence from previous trials.

Finding all relevant randomised controlled trials is undoubtedly the major challenge of systematic reviews. Inclusion of all relevant randomised trials increases the power of a systematic review to detect moderate treatment effects, and also avoids the mistaken inference that can arise when a biased selection of trials is reviewed. For example, in defence of the assertion that steroids are ineffective in the treatment of severe brain injury, a recent report cited the results of three randomised trials.2 These three trials comprised only a small proportion (three out of at least 17 trials) of …