Common Measures of Functional Capacity and Disability
Traditional measures of disability in the population have been collected in national surveys of well-defined populations for many years. The major measures include the ability or inability to perform a function as well as the difficulty of performing it and the ability to perform it without assistance. The principal metrics employed in long-term, large-scale national studies include
- Activities of daily living (ADL). These tasks required to take care of oneself, such as bathing, toileting, eating, and dressing, are usually measured as difficulty performing them or receiving help in performing them. These are measures of fairly severe disability and predict need for personal care services and residence in a nursing facility for long-term care.
- Instrumental activities of daily living (IADL). These tasks associated with the capacity to live independently, such as cooking, shopping, managing finances, and using communication devices, are measures of moderately severe disability and predict need for assistance such as homemaker and home health assistance.
- Physical limitations in activity. Examples are the ability to climb stairs, walk ¼ mile, stand or sit for prolonged periods, raise a 10 lb object over one’s head, climb steps, stoop, bend or kneel, grasp small objects, and move large objects. These limitations may reflect underlying disease and may predict capacity to participate in certain occupations.
- Cognitive function. While many aspects of behavior and cognitive function change with age, including speed of processing, changes in various vocabulary subsets, decision making, and the like, most surveys evaluating functional impairment have focused on general mental status, including orientation to time and place, working memory, attention, language, calculation, and familiarity with current affairs. For most cognitive measures that decline with age, studies show the declines to be very modest until at least age 70 and, in most cases, age 75. Thus the impact on the likelihood that this age group will participate in the workforce is minimal. Recently, Skirbekk, Loichinger, and Weber (2012) proposed the use of a cognitive-function-based measure—the cognition-adjusted dependency ratio (CAGR)—as a measure of aging in populations that avoids the pitfalls of simple age-based ratios such as an old-age dependency ratio and measures based purely on physical function.
The measurement of disability is evolving. There has been growing interest in the development of additional measures of disability that account