Active Life Expectancy

Active life expectancy (ALE) refers to the number of years of life one can be expected to live without a disability. ALE answers the question, Of the remaining years of life for this cohort of persons, what proportion is expected to be spent disability-free? As such, it is used to evaluate the quality of life rather than just the quantity. The term was first introduced by Katz and colleagues in 1983, although others had described similar concepts in the mid-1960s and early 1970s. ALE is a summary measure of population health, is based on aggregate statistics, and is used in demography and epidemiology to measure and compare the health and functional status of national populations.

ALE is usually expressed as a component of total life expectancy at a certain age. In the measurement of ALE, disability is usually defined as difficulty in performing one or more activities of daily living (ADLs), which include eating, dressing, bathing, toileting, walking, and transferring to a bed or chair. There are two closely related concepts, disability-free life expectancy (DFLE) and healthy, or health-adjusted, life expectancy (HALE). While ALE uses the presence of a limitation in any one of the activities of daily living as an endpoint, disability-free life expectancy uses the presence of limitations in either ADLs or instrumental activities of daily living (IADLs), and HALE uses a measure of general health status, or good health versus poor health.

ALE can be computed in one of two ways, by using multistate life tables or by the Sullivan method. The Sullivan method requires a period life table for the population and observed age-specific prevalence of disability in the population (πi). Using standard life table notation, at each age i, the number of person years lived in that age interval (Li) is multiplied by the proportion of people at that age who are not disabled (1-πi). ALE is the total of all person years lived above an age i divided by the number of survivors to age i, li. In contrast, the multistate life table method requires age-specific transition probabilities. These transition probabilities, usually derived from longitudinal survey data, give the rates of moving from health to disability (and back), as well as the risk of death for both the healthy and disabled states at each age. Survival models incorporate these transition probabilities to estimate the time expected to be spent in the two states, active and disabled. The advantages of the multistate method include the ability to model recovery and the ability to include covariates in the models.

This method was used in 2005 by Reynolds and colleagues to examine the effect of obesity on ALE. They found that being obese at age 70 has virtually no effect on the total number of years of life remaining but reduces ALE by 2.4 years for women and 1.5 years for men.