Development of a physical function outcome measure to harmonize comparisons between three Asian adult populations

Purpose: The purpose of this study was to use modern measurement techniques and create a precise functional status metric for Asian adults. Methods: The study subjects included Asian American adults from the 2012 Health and Retirement Study (n = 211), Chinese adults in the China Health and Retirement Longitudinal Study (n = 13,649), and Korean adults in the Korean Longitudinal Study of Aging (n = 7,486). The Rasch common-item equating method with nine self-care and mobility items from the three databases were used to create a physical function measure across the three Asian adult populations. Results: The created physical function measure included 23 self-care and mobility tasks and demonstrated acceptable psychometric properties (unidimensional, local independence, no misfit, no differential item functioning). A significant group difference in the estimated physical function across the three Asian adult populations (F_{2 , 21242} = 445.21, p < 0.0001) was identified. The American Asian adults (5.16 logits) had better physical function compared to the Chinese (4.15 logits) and Korean adults (3.32 logits). Conclusion: Since the outcome measure was calibrated with the population-representative Asian samples, this derived physical function measure can be used for cross-national comparisons between the three countries. Using this precise functional status metric can help to identify factors that influence health outcomes in other Asian countries (China and Korea). This has the potential to generate numerous benefits, such as international disability monitoring and health-related policy development, improved shared decision making, and international syntheses of research findings.