Are distinctive ethical principles required for cluster randomized controlled trials?

Cluster randomized trials are increasingly used in research into health care and health services. Ethics of individual patient randomized trials have been elucidated in a number of different codes, but less attention has been given to the ethical issues raised by cluster randomized trials. I assess the challenges raised by cluster randomized controlled trials by considering three questions: What are the essential elements of ethical medical research, particularly experiments on people? What are the features which distinguish cluster randomized controlled trials from ordinary RCTs? Do the distinctive features of cluster randomized trials entail new ethical principles, or careful application of existing principles? I conclude that cluster randomized controlled trials raise new issues on the nature and practice of informed consent, because of the levels at which consent can be sought, and for which it can be sought. In addition, careful consideration of the principles relating to the quality of the scientific design and analysis, balance of risk and benefit, liberty to leave a trial, early stopping of a trial and the power to exclude people from potential benefits is required. Copyright 2001 John Wiley & Sons, Ltd.