Assessment of function and disability in longitudinal studies.

Over the past 2 decades, there has been considerable progress in the assessment of function and disability in older persons. Tests of physical performance are now routinely included in longitudinal studies to measure functional limitations, which are considered the building blocks of functioning. In addition, new strategies have been developed to assess the presence and onset of disability and to expand the scope of disability assessments beyond traditional indicators of difficulty and dependence. Contemporary measurement technologies, such as item response theory and computer adaptive testing, show great promise in the assessment of functional status and disability, but prospective studies are needed to demonstrate their true value, particularly to identify the circumstances in which their use will improve the assessment of functional outcomes in older persons. Another high priority for future research is to validate and further refine strategies to more completely and accurately ascertain the occurrence of disability in older persons.