The level and time course of disability: Trajectories of disability in adults and young elderly

Objectives. The objectives of this study were: (i) to identify trajectories in the level and time course of disability, (ii) to determine the relative frequency of each trajectory, and (iii) to assess the relationship of these trajectories with age, sex and the presence of four chronic diseases (asthma/chronic obstructive pulmonary disease (COPD), heart disease, severe low back complaints and diabetes mellitus). Methods. We used six measurements of disability and information on mortality from a longitudinal study in Dutch persons aged 15-74. We used cluster analyses to group persons with similar levels and time courses of disability into disability trajectories. Deaths were classified into a separate trajectory. Multinomial regression was used to assess the relationship of the trajectories with age, sex and the four chronic diseases. Information on disability in the last year(s) prior to death was used to examine disability prior to death. Results. Nine trajectories of disability were identified, while all deaths were classified into a separate trajectory; 74% was entirely non-disabled. The size of the other trajectories varied from 10% (permanently mildly disabled) to 0.5% (severely disabled with large increase in disability). Significant associations were found with age and, correcting for age and sex, with asthma/COPD, heart disease and low back complaints, but not with diabetes. The ORs were generally highest for trajectories characterized by severe disability, although disease-specific associations were also found. Among the deaths, 41% of the trajectories were associated with disability prior to death. Disability prior to death was more prevalent among persons with heart disease, back complaints, and asthma/COPD. Conclusions. These findings suggest that disability is a dynamic process, and that important differences exist within the 'disabled' population. This is important for assessing the need for care and shows the limitations of modeling disability change based on two measurements only.