Hard‐To‐Reach and Hidden Groups in Health‐Related Research—A Scoping Review

The aim of this scoping review was to identify hard-to-reach and hidden groups in health-related research and to understand the recruitment methods used with these groups. The presented scoping review has an exploratory perspectiveand was conducted in accordance with Arksey and O'Malley's framework and the PRISMA-ScR guidelines. A comprehensive search of CINAHL and MEDLINE databases was performed for studies published up to November 2022. The searches were updated in December 2024. Relevant papers were identified via specific search terms and inclusion and exclusion criteria. Two authors independently assessed eligible literature and extracted relevant data, which was analysed and synthesised to answer the research questions. The analysis method used was descriptive analysis with quantification. Overall, 1024 studies were screened. The included studies were published between 2001 and 2022. A total of 41 studies were included in the review. In this data, groups were defined mostly as hard-to-reach and hidden. The groups were divided into eight categories: LGBTQ+ community, intoxicant users, sex workers and their clients, marginalised groups, mental health care seekers and users, impaired persons, people living outside their original home country and victims of abuse or neglect. Recruitment methods were varied, with snowball sampling, respondent-based sampling and websites being the most used. This review provides insight into the current knowledge on hard-to-reach and hidden study groups. In studies targeting hard-to-reach and hidden groups, the use of concepts is variable and inconsistent. In clinical nursing practice, it is important to identify hidden and hard-to-reach groups, as the goal of equality is to improve the health and well-being of all individuals, including marginalised groups. Reporting was guided by Preferred Reporting Items for Systematic Reviews and Meta-Analysis ex-tension for Scoping Reviews (PRISMA-ScR). No patient or public contribution.