[1][2] An autonomous person is defined as an individual who is capable of self-legislation and is able to make judgments and actions based on their particular set of values, preferences, and beliefs.
Other cases involve showing respect to people who for whatever reason are not free to choose among the typical range of options when making a decision.
[3][4] In medical research ethics, the term Vulnerable Populations generally refers to individuals whose situations do not allow them to protect their own interests.
[5][6] These individuals are entitled to protection, and additional ethical justification is needed to involve such populations in human subject studies.
Another justification would be that the aim of the study is to gain knowledge to improve diagnosis, prevention or treatment of diseases associated specifically with that population.