Future disability projections could be improved by connecting to the theory of a dynamic equilibrium

Objective Projections of future trends in the burden of disability could be guided by models linking disability to life expectancy, such as the dynamic equilibrium theory. This paper tests the key assumption of this theory that severe disability is associated to proximity to death whereas mild disability is not. Study Design and Setting Using data from the GLOBE study, the association of three levels of self-reported ADL disability with age and proximity to death was studied using logistic regression models. These regression estimates were used to estimate the number of life years with disability for life spans of 75 and 85 years. Results The prevalence of disability incrementally increased with approaching death with 12 percent per year for moderate disability to 19 percent for severe disability. However, no association was observed for mild disability. A ten year increase of lifespan was estimated to result in a substantial expansion of mild disability (4.6 years) compared to a small expansion of moderate (0.7 years) and severe (0.9 years) disability. Conclusion These findings support the theory of a dynamic equilibrium. Projections of the future burden of disability could be substantially improved by connecting to this theory and incorporating information on proximity to death.