Capacity is the ability of prospective or actual participants to understand relevant information presented (e.g. purpose of the research, foreseeable risks, and potential benefits), and to appreciate the potential consequences of any decision they make based upon this information. The TCPS2 states that a participant may have developing or diminished capacity, i.e. a minor or person with a cognitive impairment, but still be able to decide whether to participate in certain types of research. If a potential research participant has the capacity to consent, consent must be sought from them before the research commences. If a person does not have the capacity to consent, they should still be involved in the consent process where possible and appropriate and given the opportunity to assent. If a person who lacks the capacity to consent declines to participate in research, his or her dissent must be respected and the person may not be included in the research.
Capacity to consent to research is not a static determination; it may vary over time, and upon the complexity and circumstances of the decision being made. It is the responsibility of the Principal Investigator (PI) to determine and monitor participants' capacity to consent and to describe this to the REB in the context of the proposed study. Where it is foreseeable that a participant may lose capacity during a research project, for example in studies of cognitive impairment, it may be appropriate to ask participants to express their preferences and ensure that they have authorized a trusted person to make decisions on their behalf should they lose the capacity to provide ongoing consent.
For further information see the Tri-council Policy Statement: Ethical Conduct for Research Involving Humans (2010)