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Understanding measures of treatment effect in clinical trials
  1. A K Akobeng
  1. Correspondence to:
    Dr A K Akobeng
    Department of Paediatric Gastroenterology, Central Manchester and Manchester Children’s University Hospitals, Booth Hall Children’s Hospital, Charlestown Road, Blackley, Manchester M9 7AA, UK;


Evidence based medicine implies that healthcare professionals are expected to base their practice on the best available evidence. This means that we should acquire the necessary skills for appraising the medical literature, including the ability to understand and interpret the results of published articles. This article discusses in a simple, practical, ‘non-statistician’ fashion some of the important outcome measures used to report clinical trials comparing different treatments or interventions. Absolute and relative risk measures are explained, and their merits and demerits discussed. The article aims to encourage healthcare professionals to appreciate the use and misuse of these outcome measures and to empower them to calculate these measures themselves when, as is frequently the case, the authors of some original articles fail to present their results in a more clinically friendly format.

  • AR, absolute risk
  • ARR, absolute risk reduction
  • BPD, bronchopulmonary dysplasia
  • NNT, number needed to treat
  • RR, relative risk
  • RRR, relative risk reduction
  • RSV, respiratory syncytial virus
  • absolute risk reduction
  • clinical trial
  • evidence based medicine
  • number needed to treat
  • risk measures

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