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Quality of randomised controlled trials in head injury

BMJ 2000; 321 doi: (Published 16 September 2000) Cite this as: BMJ 2000;321:704

Statistical power can be increased

  1. Chantal W P M Hukkelhoven, epidemiologist (,
  2. Ewout W Steyerberg, epidemiologist,
  3. Andrew I R Maas, neurosurgeon
  1. Erasmus Medical Centre Rotterdam, 3000 DR Rotterdam, Netherlands
  2. Wythenshawe Hospital, Manchester M23 9LT

    EDITOR—We agree with Dickinson et al1 that larger and better designed randomised controlled trials are necessary to detect benefits of treatment in head injury.2 But increasing the sample size is not the only solution to show efficacy. The statistical power of a study can also be improved by randomising the same number of patients but taking prognostic factors, such as age or Glasgow coma scale, into account.

    Firstly, one might limit the inclusion of patients to those with an intermediate prognosis—for example, between 20% and 80% probability of a favourable outcome.3 This leads to a focus on patients for whom treatment effects can be well determined. For the same power, a reduction in sample size of 30% might be achievable.3 After showing efficacy in the intermediate risk group, …

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