Psychometric Properties of Instruments Assessing Intrinsic Capacity: A Systematic Review

Introduction: Intrinsic capacity (IC) is a multidimensional indicator proposed by the World Health Organization that encompasses mental and physical capacities associated with functional ability. With the help of IC, different pathways of aging can be better understood, and heterogeneity can be captured more effectively. Before IC can be clinically incorporated, it requires valid and usable instruments alongside a comprehensive evaluation of psychometric evidence. Therefore, the present systematic review critically appraised, compared, and summarized the measurement properties of existing IC instruments used by older people. Methods: Published studies were searched in seven databases: EMBASE, MEDLINE, PsycINFO, PubMed, ScienceDirect, Scopus, and Web of Science, until August 2022. The measurement properties of the IC measures were evaluated using the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN). Results: Of the 582 papers initially identified, 10 studies were eligible for inclusion. Seven instruments were classified as five-domain measures, and three as more than five-domain measures. No instrument assessed all nine criteria in the psychometric properties evaluation outlined by COSMIN. The most reported psychometric properties were construct validity (n = 8), measurement invariance (n = 8), and structural validity (n = 7). There was underreporting of content validity, reliability, and measurement error. Conclusion: The present review indicated a general lack of psychometric assessments of existing IC instruments with independent studies as their evidence base. There is a need to explore further the associations of IC and its five domains of interaction, which express the ability of individuals to interact with the environment and affect their functional ability.