Appropriate inclusion of adult research participants with intellectual disability: an in-depth review of guidelines and policy statements.

The history of human-subject experimentation has shown the need for safeguards to protect participants from abuse. Balancing participant protection with adequate representation of the adult intellectual disability population in research presents an important challenge. Our study aimed to analyze guidance on the appropriate inclusion of adults with intellectual disability who are or are not able to consent to biomedical research participation. Terminology, consent and type of ethically acceptable research provisions relevant to adult participants with intellectual disability were comprehensively reviewed in a selection of 17 international and national ethical research guidelines and statements. Most guidelines and statements recommend that adult participants with intellectual disability who are unable to consent be included when it is not possible to conduct the same research with adults capable of independent decision-making, or when there is therapeutic benefit and only minimal risk. Instead of naming specific requirements, the Australian statement stands out by asserting the "individual right" to participate. Assent requirements for incapacitated adults are not explicitly mentioned in most documents reviewed. There appears to be room for further description of the importance of careful capacity assessments and solid assent requirements in ethical research guidance documentation to promote meaningful participation of adults with intellectual disability.