Development and validation of Physical Disability Index and Mental Disability Index and their associations with falls among older adults

Abstract Background To enhance the precision of measuring, analyzing, and forecasting care needs for older adults with physical and/or mental disabilities, we developed the Physical Disability Index (PDI) and Mental Disability Index (MDI). Furthermore, we evaluated the reliability and validity of the PDI and MDI. Additionally, we investigate their associations with falls to further indicate the predictive validity. Methods A total of 11,621 older adults (53.1% women; mean age=83.2; SD=10.8) from 23 provinces in China were investigated in 2017-2018 to assess the reliability and validity of the PDI and MDI among older adults aged 65 to 105. Among which, 6,071 older adults with both baseline (2017-2018) and follow-up (2021) data were included in analyses to evaluate associations between the baseline health status determined by PDI and MDI and the number and severity of falls at baseline and follow-up. Cronbach's alpha was used to determine internal consistency. The convergent and divergent validity, known-group validity and concurrent validity were assessed. Multinomial logistic regression models were utilized to assess associations. Results We found satisfactory internal consistency (Cronbach’s alpha ≥0.70) of the PDI and MDI in the total sample and sex-specific subgroups. Our results support the convergent and divergent validity, known-group validity, and concurrent validity of the PDI and MDI. We also found baseline physical disability and comorbid physical and mental disability are associated with a higher risk of baseline and follow-up falls. Conclusions The PDI and MDI are reliable and valid instruments to assess physical and mental disability status among older adults respectively.