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Clinical equipoise and not the uncertainty principle is the moral underpinning of the randomised controlled trialForAgainst

BMJ 2000; 321 doi: (Published 23 September 2000) Cite this as: BMJ 2000;321:756

Clinical equipoise and not the uncertainty principle is the moral underpinning of the randomised controlled trial

The ethical basis for entering patients in randomised controlled trials is under debate. Some doctors espouse the uncertainty principle whereby randomisation to treatment is acceptable when an individual doctor is genuinely unsure which treatment is best for a patient. Others believe that clinical equipoise, reflecting collective professional uncertainty over treatment, is the soundest ethical criterion. Here doctors from two Canadian centres discuss their positions.


  1. Charles Weijer, assistant professor of medicine (,
  2. Stanley H Shapiro, professorb,
  3. Kathleen Cranley Glass, assistant professorc
  1. a Department of Bioethics, Dalhousie University, Halifax, NS B3H 4H7, Canada
  2. b Department of Epidemiology and Biostatistics, McGill University, Montreal H3A 1A2, Canada
  3. c Biomedical Ethics Unit, Department of Human Genetics and Department of Pediatrics, McGill University
  4. Departments of Obstetrics and Gynaecology, Clinical Epidemiology, and Biostatistics, McMaster University, Hamilton, ON, Canada L8N 3Z5
  1. Correspondence to: C Weijer

    On what ethical grounds may a physician offer trial participation to his or her patient? The answer seems to depend greatly on which side of the Atlantic you reside. In the United Kingdom, the uncertainty principle is widely endorsed. 1 2 However, in North America, clinical equipoise—reflecting collective uncertainty—is the dominant ethical basis.3 Which of these principles offers the preferred moral underpinning for the randomised controlled trial?

    It is widely acknowledged that physicians have a primary duty to promote their patients' welfare. When physicians become investigators, however, other ends such as recruiting enough subjects and retaining them in the trial may conflict with this duty.4 How can the physician maintain fidelity to the patient and further the ends of a randomised controlled trial? The uncertainty principle offers an appealing solution to this problem.

    Uncertainty principle

    Physicians who are convinced that one treatment is better than another for a particular patient cannot ethically choose at random which treatment to give, they must do what they think best for the patient. For this reason, physicians who feel they already know the answer cannot enter their patients into a trial. If they think, whether for a wise or silly reason, that they know the answer before the trial starts, they should not enter any patients.2

    On the other hand, if the physician is uncertain about which treatment is best for a patient, offering the patient randomisation to equally …

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