Disability severity transitions in the community-dwelling Swiss ageing population: secondary analysis of the Swiss version of the Survey of Health, Ageing and Retirement in Europe (SHARE) using multistate models

Objective To describe disability severity transitions in the ageing population in Switzerland using an overall functioning score to define four disability severity states (no, mild, moderate and severe) and death, and to investigate the association of multimorbidity and further predictors with these transitions. Design Secondary analysis of the Swiss version of the Survey of Health, Ageing and Retirement in Europe (SHARE). Setting Switzerland. Participants Community-dwelling population aged 50+ with at least two interviews in SHARE (N=3505). Interventions Not applicable. Main outcome measures and methods Primary outcome measures are the disability severity as assessed by a previously developed overall functioning score, and death status as assessed by the SHARE end-of-life interview. Transition analysis between disability severity states and death was conducted using multistate Markov models. The association between predictor variables and transition intensities was quantified using the proportional hazards assumption. Two distinct operationalisations of multimorbidity (count, burden) were used and analysed according to two separate models (A, B). Results The findings for both models were similar: Estimated HRs for transition intensities suggest that being multimorbid or having a higher disease burden score increases the risk of transitioning to higher disability severity states and death for most transitions (HRs between 0.90 and 2.34 for model A compared with not being multimorbid; HRs between 0.95 and 1.46 for model B for a one-point increase in the disease burden score). In addition, most transitions to higher disability severity states and death are more likely for higher age (HRs between 1.00 and 1.14 for model A, and between 1.00 and 1.15 for model B for a 1 year increase in age), and transitions to death are less likely for women, compared with men (HRs between 0.34 and 0.88 for model A, and between 0.38 and 0.71 for model B). Conclusions This study is a first attempt to understand disability severity transitions in the older population in Switzerland. Although we believe that such an approach is suitable to inform resource allocation to LTC, rehabilitation and prevention, more detailed information on contextual factors will be important to consider for future research. Moreover, our study contributes to the discussion on how to operationalise multimorbidity in healthy ageing research.