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controlled trial

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Controlled trial

  • an experimental study in which an intervention is applied to one group of subjects and the outcome of interest is compared with that in an otherwise identical control group who received another intervention (such as another active treatment or placebo) at the same time
  • if possible, subjects are assigned to treatment in a random way such that neither the subject nor the investigator knows which intervention the subject is receiving (this would be termed a double-blind randomised controlled trial)
  • study outcomes
    • primary outcomes are determined before patients are entered into study and are focused on predicted benefits and risks
  • often these studies employ strict criteria for the inclusion and exclusion of subjects, which can lead to difficulties in extrapolating their results to wider populations seen in clinical practice
  • follow-up
    • often have short follow-up because of costs and pressure to produce timely evidence


  1. MeReC Briefing (2005);30 (supplement):1-7.
  2. Rochon PA et al.Reader's guide to critical appraisal of cohort studies: 1. Role and design. BMJ 2005;330:895-7.