EDITOR—The review by Dickinson and colleagues1 shows a remarkably narrow view of research in head injury and virtually ignores the need to match the design to the research question. Historically, many clinical trials have been underpowered, but the authors' premise that the main aim of head injury trials should be to detect changes of “a few per cent” in the rate of death or disability does not apply, for example, to phase I/II trials in the acute stage nor the later interventions used in many of their reviewed trials. The authors might find it useful to reread the article “Why do we need some large, simple randomized trials?” by Yusuf et al (note the word “some” in the title).2

Several factors influence the relevant effect size and hence the size of the trial. Some potentially powerful interventions in severe head injury are not widely practicable and are likely to be expensive, and therefore evidence of a substantial effect is required if budget holders are to be persuaded to support them. The focus on a 10% benefit has reflected a perception that funding could be obtained for a treatment that benefits 1 person in 10. However, even this may be optimistic. Despite the 13% benefit obtained from nimodipine treatment in subarachnoid haemorrhage,3 corresponding to a number needed to treat of eight, clinicians have had difficulties in gaining funding for the routine use of this drug. The …