Discriminative validity of the Core Outcome Set Physical Self-Sufficiency in a Population of Older Adults

Abstract

Aim To assess the discriminative validity of the Core Outcome Set Physical Self-Sufficiency (PSS) in a population of Dutch older adults ( 65 years) with different levels of PSS. Secondary objective was to assess to what extent the domains ‘coping’, ‘empowerment’ and ‘health literacy’ contribute to the Core Outcome Set PSS in addition to the domain ‘physical capacity’ in a population of Dutch older adults. Methods This validation study had a cross-sectional design. A population of 200 community-dwelling older adults and older adults recruited in residential care facilities were evaluated by the Core Outcome Set PSS and a reference variable for PSS. The Core Outcome Set PSS contains measurements on the four domains of PSS: physical capacity, coping, empowerment and health literacy. Because no gold standard for PSS exists, a proxy indicator was used: group membership based on help needed in (instrumental) activities of daily living ((i)ADL) and living situation, resulting in three groups. Ordinal logistic regression was used with main outcome prediction accuracy of the Core Outcome Set PSS on the proxy indicator for PSS. Results The model based on the Core Outcome Set PSS had an overall prediction accuracy of 68 percent. For older adults living at home and depending on help in (i)ADL, prediction accuracy was 58 percent. Only physical capacity measured with Short Physical Performance Battery was significantly associated with group membership. Adding health literacy with coping or empowerment to a model with physical capacity improved the model significantly (p<0.01). Conclusion Physical Self-Sufficiency can be measured with the Core Outcome Set PSS. Discriminative validity of the Core Outcome Set PSS is moderate. A model including physical capacity, health literacy and coping seems to be optimal, based on the current composition of measurement instruments. Clinical Relevance It is recommended to remove the measurement of empowerment from the Core Outcome Set PSS. Furthermore, other factors, like environmental aspects, seem to be important to incorporate before using the Core Outcome Set PSS in further research or in clinical practice.