The membership composition of a REC is fundamental to ensuring that it has the range of expertise and the breadth of experience necessary to provide competent and rigorous ethics review of the submitted research proposals, and to do so from a position that is independent of both the researchers and the RO in which it is located. Its composition and independence are important in establishing the legitimacy of the opinions expressed and the decisions made, in the eyes of the community and wider society as well as the researchers and funders of research.

Principal RECs should be multidisciplinary and comprised of both men and women. They should include at least one external member with no affiliation to the RO in question. There should be a chairperson and members who have broad experience and expertise in the areas of research regularly reviewed by the REC, and members who have the confidence and esteem of the research community. Principal RECs would also benefit from including individuals who reflect ethnic diversity, users of specialist health, education or social services (where these are the focus of research activities), individuals with experience of professional care or counselling, and individuals with specific methodological expertise (for example, quantitative or qualitative methods) relevant to the research they review. A principal REC should include among its membership people who are collectively familiar with a range of philosophical approaches to research ethics and with the different perspectives seen in individual research proposals. Taking all of this into account, good practice would suggest that a ROs principal REC would need at least seven members.

A REC may seek advice and assistance from experts outside the committee in considering a research proposal. When this happens, the chair should establish that the experts have no conflict of interest in relation to the proposal.