The basic principles of ethical research as laid out in the Belmont Report  include “respect for persons”, which stipulates that all individuals should be treated as autonomous agents. Typically this principle is translated into practice with a statement read to all study subjects concerning the voluntary nature of study participation and the freedom to withhold consent. These ethical guidelines largely derive from medical trials where individual targeting of an intervention such as an experimental drug is typical. Often for impact evaluations in the social sciences, however, it is very common for the intervention to target a village, district, or other community structure. What happens to individual consent and the “respect for persons” in these cases? Is individual consent even possible or desirable?
A cluster or group trial is typically the design choice when individual targeting of an intervention is impossible either due to the aggregate nature of the intervention technology, such as a district level health systems intervention , or the very real possibility of spillovers, such as a media campaign targeted at political participation . While the decision to cluster a trial is an obvious choice to the researcher, it does present unique challenges to the ethical principle of “respect for persons”.
In cluster studies it is very difficult or impossible to obtain informed consent from every individual potentially exposed to the intervention (note that the consent here refers to consent to study participation rather than consent to a survey interview – interview consent must be sought separately and is typically offered only to the subset of study subjects surveyed). Furthermore, in these cases it is not clear what study refusal would mean. In an individual trial, refusal of consent excludes the subject from study participation. If individual consent is sought for a cluster trial, should the refusal of one individual invalidate the participation of the whole community? Most researchers would probably say no.
Given the impossibility of comprehensive individual consent, the cluster study design inherently contrasts individual autonomy with potential social benefits and these trade-offs must be weighed by the research team and the ethical review committee. Some suggest that the difficulties of obtaining individual consent combined with a low risk of harm form the intervention may render the need for consent null and void .
More commonly, mechanisms have been developed that seek consent from representative individuals in the study community. These representatives vary widely across studies in part due to the nature of the intervention. Examples of community representatives include include village elders, local government officials, heads of village organizations such as the village development committee or neighborhood health committee, and respected community members such as doctors or teachers.
There are few guidelines over the choice of community or cluster representation. Presumably the community representative should “represent” the community in a legitimate capacity with respect to study consent. However some community representatives are democratically elected while others are selected through a non-participatory process such as heredity. Do the means of representative selection affect the legitimacy of group consent? Even if their representation is seen as “legitimate” by the community, community representatives may be drawn from local elites that can have individual interests either unrelated or even contrary to the intended beneficiaries of the intervention. For example an anti-poverty public works program may divert low wage labor from traditional sources of local employment. An intervention targeted to women’s health may find that all traditional community representatives are male. In these cases, is a requirement of consent from community representatives desirable?
Some studies also hold community meetings to introduce and describe the study and give the community the opportunity to question the researchers. At the end of these meetings something like community consent is sought through a general discussion. However this is not a universal practice. Should it be? If not, when can a requirement of community meetings be waived? And how exactly should a community be defined?
Finally, what to do about control communities that don’t receive any attention from researchers besides survey activities? If the use of a control is deemed ethical , do researchers have an equal obligation to seek study consent from the control communities? It is possible that the mere mention of a study in which the selected community is to serve as a control may lead to community resentment. In the extreme case, this resentment and associated behaviors can even invalidate the study design through negative spillovers.
There are many questions and few specific guidelines. One representative guideline from The Council for International Organizations of Medical Sciences is found in their 1991 International Guidelines for Ethical Review of Epidemiological Studies . Note that while the general principle is clear, the conduct of cluster consent is, perhaps necessarily, vague:
“When it is not possible to request informed consent from every individual to be studied, the agreement of a representative of a community or group may be sought, but the representative should be chosen according to the nature, traditions, and political philosophy of the community or group. Approval given by a community representative should be consistent with general ethical principles. When investigators work with communities, they will consider communal rights and protection as they would individual rights and protection. For communities in which collective decision making is customary, communal leaders can express the collective will.”
Right now cluster consent issues are tackled separately by each researcher and each ethical review board. For an individual study, the review board is an important arbiter on the appropriate form of cluster consent. However the research community can promote more uniformity of practice and awareness through the dissemination of results. As Osrin and co-authors write , “at the minimum we need to document the choice of [community] representatives and the reason for approaching them”. Furthermore, Donner and Klar suggest  journal editors should stipulate that any cluster trial needs to report institutional review board approval and how issues of participant consent were resolved. These actions, while falling short of stipulating concrete guidelines, would highlight the difficulties and complexities around the issue and help promote wider discussion and understanding.