Measures of identity in adolescents/young adults with long-term physical health conditions: A systematic review

Objective: We identified and evaluated measures of identity used with adolescents/young adults aged 16–24 years living with long-term physical health conditions (LTC-P), focusing on the conceptualisation, development, and psychometric properties of measures. Review funded by Sir Halley Stewart Trust and the University of Bath. Review protocol: https://osf.io/bhkze. <br/>Methods: Five databases (APA PsychNET, PubMed, Web of Science, SCOPUS, CINAHL) were searched. Studies were included if they were peer-reviewed, reported participants aged 16–24 with LTC-P, and used a quantitative identity measure. Psychometric properties and risk of bias were evaluated using COSMIN quality criteria, and content validity was reviewed narratively. Data analysis and synthesis followed COSMIN methodology for reviews.<br/>Results: Thirty-eight papers met inclusion criteria, involving 9,663 participants and 16 identity measures. Across the papers, identity was defined and conceptualised in varied ways. Only three measures; the Illness Identity Questionnaire (IIQ), Dimensions of Identity Development Scale (DIDS), and Identity Motives Scale (IMS), were used in multiple studies and assessed for psychometric quality. Evaluated properties included structural validity, internal consistency, measurement invariance, and construct validity. The IIQ and DIDS were tentatively recommended for use. The IMS was rated as needing further validation due to limited content validity. <br/>Conclusions: The IIQ and DIDS may be appropriate when their conceptual focus aligns with research objectives. Remaining measures should be used cautiously; many lack developmental or condition-specific relevance. Future identity measure development should integrate lived experience, expert input, and rigorous psychometric testing to ensure tools are both meaningful and fit for purpose in target populations.