The rules of research ethics are to make sure people who are the subject of the research are protected from harm during the research process. This can mean leaving them out of the research project because the ethics approval process is so onerous. So who decides which groups are ‘vulnerable’ group and those that are not?
Vulnerable groups involve people considered susceptible to coercion or undue influence in a research setting. They may be people who are incapable of understanding what it means to participate in research. Or they might not understand what constitutes informed consent.

Individuals considered vulnerable might have a diminished capacity to anticipate, cope with, resist, and/or recover from the impact of a natural or constructed hazard. Vulnerable groups may also consist of individuals who are unable to care for themselves and/or may have an increased chance of suicide, self-harm, or the likelihood of harming others.
A Sage special issue on research methods looks at the various issues relating to researching vulnerable groups. The open access issue is titled, Ethics and Consent in Research with Vulnerable Participants. There is good advice here.
In some cases, involving the people from the nominated vulnerable group to be part of the research team and the processes is another way to conduct the research. See the section on Co-design Processes for more.
Informed consent
How do you know when the participant really understands consent to participate? An article titled, Obtaining Informed Consent of Vulnerable Populations for Participating in Social and Education Sciences Research, looks at the issues.
From the abstract: Obtaining informed consent is the foundation of ethics in clinical research involving human participants. The “Common Rule” identifies “vulnerable subjects” as “children, prisoners, individuals with impaired decision-making capacity, or economically or educational disadvantaged persons.”
This article explores a pragmatic approach for Institutional Review Boards to review research protocols involving individuals with disabilities and/or those who are educationally-disadvantaged as study participants. As a direct result, we formed a process for obtaining informed consent of vulnerable participants in social and education sciences research.
Navigating ethical challenges
Mary Quirk brings an “Inclusion as Process” approach to ethical issues in her doctoral study involving people with disability. Her article is based on a case study where she relates her experience in the first person.
In her doctoral research, Quirk adopted Universal Design and Universal Design for Learning approaches as a way to engage in inclusive research. The aim was to facilitate the voices of people with disabilities in education during the COVID-19 Pandemic.

The title of the paper is, How to Adopt an “Inclusion as Process” Approach and Navigate Ethical Challenges in Research. Also available through Sage Publications. Mary Quirk is based at Trinity College Dublin, Ireland.
From the abstract
The case study explains “Inclusion as Process” as an approach to research. It discusses ethical implications of relevance to educational and other researchers. In particular, it examines the application of Universal Design (UD) and Universal Design for Learning (UDL) thinking in research and how these approaches relate to these individual yet interdependent themes. Finally, the case study outlines an “Inclusion as Process” framework to guide inclusive research.