Can we ensure that all research subjects give valid consent?

To ensure that research subjects provide valid consent, most commentators direct clinical investigators to formally assess potential subjects who are at increased risk for lacking the capacity to consent. Current data reveal, however, that subjects with no known cognitive impairments often fail to give valid consent. These data imply that the prevailing focus on individuals' capacity to consent is too narrow. To protect subjects, as well as the integrity of clinical research, the actual consent of all subjects should be formally assessed. Recent development of several preliminary consent assessment tools suggests that, in addition to being ethically preferable, with additional research this approach may be practically feasible. Future research should focus on developing a postdecision questionnaire that can be adapted to individual studies and used to assess the voluntariness and understanding of all research subjects.