ASSeTS: a systematic review and development of the World Health Organization's classification system for social isolation and loneliness interventions.

Background: Social isolation and loneliness (SIL) have emerged as critical population health concerns linked to various adverse health outcomes, including cardiovascular disease, stroke, dementia, depression, and premature mortality. However, the absence of a standard categorization for interventions aimed at reducing SIL has impeded consistent comparison, evaluation, and the accumulation of knowledge, affecting evidence-based policy decisions. To address this gap, we developed and empirically evaluated the ASSeTS (Access, Skills, Social engagement, Therapeutic and psychological, Systemic) classification system, a standardized approach for categorizing SIL interventions.

Methods: We conducted a systematic review to identify and evaluate existing classification systems used for SIL interventions. Seventeen databases were searched from inception to September 2023, with no language restrictions. Inclusion criteria encompassed established and widely used reviews with clear intervention categorizations and broad applicability to general population groups. Expert consultations supplemented the systematic review, providing iterative feedback and additional relevant literature missed from the literature search, to inform the development of the ASSeTS classification framework. The developed ASSeTS system was empirically tested by independent experts for clarity, applicability, and reliability, with inter-rater agreement assessed using Fleiss' kappa.

Results: The review identified 11 studies covering a range of SIL intervention categorization approaches. Based on synthesis and expert feedback, the ASSeTS system was structured into five main categories: Access, Skills, Social engagement, Therapeutic and psychological, and Systemic interventions. Empirical testing yielded moderate inter-rater reliability (κ = 0.419), indicating acceptable usability among expert raters. Higher agreement was found for categories such as therapeutic and psychological interventions, whereas systemic interventions showed lower reliability, suggesting opportunities for future refinement.

Conclusion: The ASSeTS classification system provides a much-needed standardized framework for categorizing SIL interventions, facilitating comparability, rigorous evaluation, cumulative knowledge, and evidence-based policy decisions. Future work should focus on refining less reliable categories, validating ASSeTS across various contexts, and integrating it into global policy frameworks to more effectively address the public health implications of SIL.