Skip to main content
When Is Informed Consent Required in Cluster Randomized Trials in Health Research?
Trials (2011)
  • Andrew D. McRae, The University of Western Ontario
  • Charles Weijer, The University of Western Ontario
  • Ariella Binik, The University of Western Ontario
  • Jeremy M. Grimshaw, University of Ottawa
  • Robert Boruch, University of Pennsylvania
  • Jamie C. Brehaut, University of Ottawa
  • Allan Donner, The University of Western Ontario
  • Martin P Eccles, Newcastle University
  • Raphael Saginur, University of Ottawa
  • Angela White, The University of Western Ontario
  • Monica Taljaard, The University of Western Ontario

This article is part of a series of papers examining ethical issues in cluster randomized trials (CRTs) in health research. In the introductory paper in this series, we set out six areas of inquiry that must be addressed if the cluster trial is to be set on a firm ethical foundation. This paper addresses the second of the questions posed, namely, from whom, when, and how must informed consent be obtained in CRTs in health research? The ethical principle of respect for persons implies that researchers are generally obligated to obtain the informed consent of research subjects. Aspects of CRT design, including cluster randomization, cluster level interventions, and cluster size, present challenges to obtaining informed consent. Here we address five questions related to consent and CRTs: How can a study proceed if informed consent is not possible? Is consent to randomization always required? What information must be disclosed to potential subjects if their cluster has already been randomized? Is passive consent a valid substitute for informed consent? Do health professionals have a moral obligation to participate as subjects in CRTs designed to improve professional practice?

We set out a framework based on the moral foundations of informed consent and international regulatory provisions to address each of these questions. First, when informed consent is not possible, a study may proceed if a research ethics committee is satisfied that conditions for a waiver of consent are satisfied. Second, informed consent to randomization may not be required if it is not possible to approach subjects at the time of randomization. Third, when potential subjects are approached after cluster randomization, they must be provided with a detailed description of the interventions in the trial arm to which their cluster has been randomized; detailed information on interventions in other trial arms need not be provided. Fourth, while passive consent may serve a variety of practical ends, it is not a substitute for valid informed consent. Fifth, while health professionals may have a moral obligation to participate as subjects in research, this does not diminish the necessity of informed consent to study participation.

  • Informed consent,
  • Cluster randomized trial,
  • Health research
Publication Date
September 9, 2011
Citation Information
Andrew D. McRae, Charles Weijer, Ariella Binik, Jeremy M. Grimshaw, et al.. "When Is Informed Consent Required in Cluster Randomized Trials in Health Research?" Trials Vol. 12 Iss. 202 (2011)
Available at: