Table 3.

Types of involvement, definitions identified by expert panellists.

Type of involvement	Consensus that this is involvement?	Agreed definition
Type 1: Young People's Advisory Group	Yes	A group or panel for consulting young people, sometimes with lived experience of mental health issues, convened to inform research activity. Young people share their views and experiences as well as providing advice and feedback to researchers to make meaningful contributions to improve research and inform decision making, either on a project specific, or regular and ongoing, basis.
Type 2: Coproduction (including codesign and cocreation)	Yes	A process of active involvement and collaboration with young people, either as a collective or individually, throughout the research process (from inception and creation to implementation and dissemination)—starting from scratch/a blank page. Following the 5 coproduction principles, young people are equal and reciprocal partners, gaining benefit themselves and working alongside researchers, having a say about how the research is done and being part of decision‐making.
Type 3: Consultation or advisory role	Yes	Young people's views and expertise are sought in relation to a project either on a one‐off or ongoing basis. Input is often limited in scope and the young people's advice may or may not be acted upon. In this sense, the young people are not equal and reciprocal partners in the research in the same way as in coproduction.
Type 4: Coresearch/peer‐research	Yes	Young people are very actively involved in key stages of the research process, bringing lived experience to the research and conducting research themselves, with the supervision of a senior researcher. A slightly more involved role than coproduction. This could be done through an internship, bursary or a voluntary or paid opportunity.
Type 5: Patient and Public Involvement	Yes	An umbrella term for coproduction and codesign which involves activities that add value or knowledge to the project through seeking the advice and opinion of young people, who would be affected by the research, on a piece of mental health research.
Type 6: Young person/peer‐led involvement and research	Yes	Young people, with lived experience, take charge of all aspects of the research process: leading, having ownership, meaningful involvement and making decisions across all stages of the research process. Researchers provide supervision and support but there is reciprocity and power is equally shared with the young people.
Type 7: Reviewer	Yes	Young people review or evaluate research documents, potentially as part of a panel of reviewers, and provide feedback and recommendations.
Type 8: Young people's involvement network/community of practice	Yes	A youth‐focused approach to involvement which can make different types of involvement more meaningful. Networks or communities of young people who have an interest in being involved in research are developed. Some networks act as a vehicle for young people to find out about opportunities or they can be groups that meet regularly for young people to direct the involvement process and decide which research questions should be addressed, and types of involvement to engage in. They are a resource for young people to learn about new opportunities to get involved.
Type 9: Young people as participants	No	Young people participate in research, as a study subject or service‐user.
Type 10: Young persons' representative on a scientific committee	Yes	For example, young people being representatives on a thesis committee or steering committee.
Type 11: Involvement ambassadors	Yes	Young people (from communities who are all too often easily ignored) are set up as involvement champions in health care research.
Type 12: Dissemination	No	Feeding back results of research to participants and the broader community.

Note: A more detailed table with example involvement activities and illustrative participant quotes is provided in Appendix S3.