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 article tests the key assumption of this theory that severe disability is associated with proximity to death, whereas mild disability is not.


METHODS
Using data from the GLOBE study (Gezondheid en Levensomstandigheden Bevolking Eindhoven en omstreken), the association of three levels of self-reported disabilities in activities of daily living with age and proximity to death was studied using logistic regression models. Regression estimates were used to estimate the number of life years with disability for life spans of 75 and 85 years.


RESULTS
Odds ratios of 0.976 (not significant) for mild disability, 1.137 for moderate disability, and 1.231 for severe disability showed a stronger effect of proximity to death for more severe levels of disability. A 10-year increase of life span was estimated to result in a substantial expansion of mild disability (4.6 years) compared with a small expansion of moderate (0.7 years) and severe (0.9 years) disability.


CONCLUSIONS
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.
Klijs
Bart
B
Department of Public health, Erasmus MC, University Medical Center, Rotterdam, The Netherlands. b.klijs@erasmusmc.nl
Mackenbach
Johan P
JP
Kunst
Anton E
AE
D000203:Activities of Daily Living; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D006233:Persons with Disabilities / Q000706:statistics & numerical data*; D005260:Female; D005544:Forecasting / Q000379:methods*; D006305:Health Status Indicators; D006801:Humans; D008017:Life Expectancy / Q000639:trends*; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D012044:Regression Analysis; D012720:Severity of Illness Index