Vulnerable Populations or Circumstances resulting in vulnerability to coercion, manipulation, or undue influence and reduced or limited voluntariness may include:

• Children/minors have a wide range of capacity depending on age, maturity and psychological state. There is potential for control, coercion, undue influence, or manipulation by parents, guardians, or investigators, particularly of young children.
• Pregnant women (the concern is focused on the fetus)
• Prisoners "A prisoner means any individual involuntarily confined or detained in a penal institution. The term is intended to encompass individuals sentenced to such an institution under criminal or civil statute, individuals detained in other facilities by virtue of statutes or commitment procedures which provide alternatives to criminal prosecution or incarceration in a penal institution, and individuals detained pending arraignment, trial, or sentencing." Included are those in hospitals or alcohol and drug treatment facilities under court order. Individuals in work-release programs and in at-home detention programs also qualify as prisoners. The definition applies to minors as well as to adults.
• Mentally Disabled Individuals have problems with capacity, which may be continuous or fluctuating, depending on the disability. In addition, they may have limitations on voluntariness because often they are institutionalized or hospitalized, are economically and educationally disadvantaged, and suffer from chronic diseases. As a result, they are potentially subject to control, coercion, undue influence, or manipulation.
• Educationally Disadvantaged Subjects may have limitations on understanding of the study they will participate in, and may even be illiterate. The possibility exists for undue influence and/or manipulation.
• Economically Disadvantaged Subjects may be vulnerable due to a limitation on voluntariness. They may enroll in research only to receive monetary compensation, or they may enroll in research to obtain medical care they cannot otherwise afford. There is potential for undue influence or manipulation.
• Marginalized Social Groups may lack influence in society as a result of race, age, disease, sexual orientation, or caste systems. These groups often do not have full access to social institutions such as the legal system. There is potential for control, coercion, undue influence, or manipulation.
• Individuals with Incurable or Fatal Diseases often have limitations on voluntariness, and in addition may have problems with capacity caused by disease or medications. These individuals may accept very high risks in desperation for a cure, even when there is little or no prospect of direct benefit.
• Emergency Situations can create a situation where capacity and voluntariness is compromised. There are often limitations to capacity due to the emergency condition. There are often limitations on voluntariness due to time constraints or hospitalization. An example is research on heart attack medications, in which the subjects are asked to consent in the ambulance on the way to the hospital. There is potential for control, coercion, undue influence, or manipulation.
• Hierarchical Social Structures that confront hospitalized patients, nursing home residents, employees, students, prisoners, military personnel, and some ethnic groups can create situations where voluntariness can be compromised. There is potential for control, coercion, undue influence, or manipulation.

(this list comes from Kenyon College's IRB website)