NBAC specifically states a person may be vulnerable "because they have difficulty providing voluntary, informed consent arising from limitations in decision-making capacity ... or situational circumstances ..., or because they are especially at risk for exploitation" While high potential for individual benefit from participating in research might increase the likelihood that a person might participate despite high risks, the root cause of their vulnerability is the potential for exploitation.

Next, the NBAC looked at characteristics individuals might have that would prevent them from being able to provide voluntary informed consent. The traits may be thought of as falling into six broad areas: cognitive or communicative, institutional, deferential, medical, economic, and social.