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Ethics in Cluster Randomised Trials

Posted on 27th May 2014 by

Learning Resources
clustering populations

First: The 4 principles of ethics

Biomedical research often involves many ethical issues, and four basic principles have been established and are intended to create a common basis of ethics despite the fact that there may be different points of view on morality. These principles are: respect for people´s autonomy, beneficence, non-maleficence and justice. Respect for autonomy implies that patients or subjects must be involved, and are free to decide about their health decisions, where informed consent is necessary to perform any procedure for them. The principles of beneficence and non-maleficence oblige us to investigate and do what is best for every patient, and act in order to provide more benefits than harms. Fair distribution of health resources constitutes the principle of justice. Despite these four established principles it´s not always clear how to define the correct ethical approach in some situations. This is often the case for randomised trials…

Randomised Controlled Trial (RCT) vs Cluster Randomised Trial (CRT)

A randomised controlled trial (RCT) is a kind of study where a particular treatment that needs to be tested is given to individual patients in a “treatment group” and they are compared to another group receiving a placebo or another treatment named the “control group”. Some circumstances require that researchers work with groups rather than individual persons: 1) when the intervention affect groups or an entire population in case of public health interventions, for example chlorine water 2) when the study may be contaminated because of communication between control and the treatment group for example behavioural and educational interventions 3) When the outcome in a single participant is modified by the “herd effect” a classic example is that vaccinating in a group makes each participant less likely to develop a disease but this effect may also be due to the group immunity. In such cases researchers perform “cluster randomised trial” (CRT) where groups or “clusters” are randomised rather than individual patients.  These groups may be neighbourhoods, schools, hospitals, prisons etc. However, cluster randomised trials may lead to many ethical issues.

What has been done about ethics in Controlled Randomised Trials?

The Rotman Institute of Philosophy put together philosophers and scientists to discuss many ethical problems in scientific research and also discuss the case of cluster randomised trials. As in a cluster randomised trial intervention and outcome are not necessarily made on the same subject for example evaluating measures as training in health practitioners and measuring outcome in patients, the research participant are not always easily known, then who gives informed consent? Is it necessary for all the participants of the cluster to give the informed consent? When is it possible to waive the informed consent? Will the study benefit the community population involved? The Rotman Institute published “the Ottawa statement on the ethics design and conduct of cluster randomised trials” the first guideline ever written about this topic.


  1. Gillon R. Medical ethics: four principles plus attention to scope. BMJ july 1994;309:184-188.
  2. Edwards S J L, Braunholtz DA, Lilford J R, Stevens J A. Ethical issues in the design and conduct of the cluster randomized controlled trials. BMJ May 1999;318:1407-1409.
  3. Weiher C, Grimshaw M J, Taljaard M, Binik A, Boruch R, Brehaut C J, et-al. Ethical issues posed by cluster randomized trials in health research. Trials 2011;12:100.


Ashline Amilcar

My name is Ashline Amilcar, I am a fourth year medical student at Universidad Autónoma Metropolitana, Mexico City. I am specially interested in endocrine regulation of human growth and molecular mechanisms of metabolic syndrome. When I am not studying I like to read and go running. View more posts from Ashline

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