Dr. Gill provided an overview of measurement of physical functioning in late-life. He explained that disability assessments can differ in several ways. First, different tasks may be included, including basic ADLs, IADLs, mobility, etc. Second, participants can be asked whether they have difficulty with a task or whether they need or get help for a task. Third, the help may be from another person or from special equipment and may or may not include supervision. Fourth, a preamble may be included in an attempt to narrow the scope of the questions (e.g., Because of a health or physical problem, do you ). Finally, the frame of reference may differ (i.e., participants can be asked whether they have disability at the present time, during the past month, usually, etc.). Estimates of disability prevalence and incidence can vary considerably based on these differences.
He recommended that when deciding between different disability assessments, investigators should consider whether the goal of the assessment is to detect change over time or to discriminate among individuals at a single point in time. Another important consideration is whether the specific questions can be administered and answered reliably, especially to proxy respondents. Because of the importance of the actual wording, the specific disability questions should be provided in published reports. Whenever possible, decisions to choose one disability assessment over another should be empirically based.
Dr. Gill went on to describe several empirical studies that may help guide decisions about disability measures. In one study, investigators at Yale investigated the distinctions between reports of difficulty and dependence in daily activities. The investigators used data from an NIA-sponsored, population-based cohort of 1,065 community living persons, aged 72 years and older. The investigators found that older persons who were independent but reported difficulty had functional profiles, physical performance scores, and rates of health care utilization and death that were intermediate to those of persons who were independent without difficulty and persons who were dependent. These findings suggest that questions about difficulty and dependence provide complementary information. Clinicians and investigators can depict the continuum of disability more fully by including questions about both difficulty and dependence in their clinical practice and epidemiologic studies, respectively.
The Yale Precipitating Events Project Study, an ongoing study of 754 initially nondisabled, community living persons, aged > 70 years, with a median follow-up (to date) of 72 months, has also provided important insights into disability measurement issues. Participants have completed comprehensive home-based assessments at baseline and, subsequently, at 18-month intervals and have been followed monthly via telephone interviews to reassess their functional status and identify admissions to the nursing home and deaths. Dr. Gill and colleagues have evaluated whether assessing disability at the present time leads to underestimates of short-term disability. Among a subgroup of 186 participants who had no disability at the present time in bathing, walking, dressing and transferring, they found that only two (1.1%) reported disability at any time during the last month. Investigators have also recently added items for proxy respondents (from the National Mortality Followback Survey). This information, together with the prospective reports from respondents, can be used to determine whether proxy informants can accurately report the occurrence of disability among decedents in the last year of life.
The second half of Dr. Gills presentation focused on physical performance measures. A physical performance measure is an assessment in which an individual is asked to perform a specific task and is evaluated in an objective, standardized manner using predetermined criteria, which may include counting of repetitions or timing of the activity as appropriate. Physical performance measures usually assess functional limitations, rather than disability per se.
The Short Physical Performance Battery (SPPB) has become the most commonly employed physical performance test in epidemiologic studies and clinical trials. The SPPB has several attractive features, including: well validated, sensitive to clinically meaningful changes, relatively portable (i.e., can be performed in home or office), and a CD-ROM instructional manual is available. Components of the SPPB and the composite battery have high predictive validity for mortality, nursing home admission, and incident disability. Most of the predictive accuracy of the SPPB is attributable to the gait speed component, which according to numerous studies is the single best predictor of disability and functional decline. Data from the Iowa EPESE demonstrate that the change scores over four years for the SPPB are normally distributed. Changes in SPPB appear to be responsive to change. For example, increasing levels of depressive symptoms were found to be associated with greater physical decline and a randomized trail of a home-based exercise intervention resulted in changes in SPPB (but not the Physical Performance Test, an alternative measure of physical performance). Finally, data from the Womens Health and Aging Study have demonstrated high test-retest reliability for the SPPB and its three components; data from the National Health and Nutrition Examination Survey (NHANES) III (1988-1994) suggests reliability for tandem stand was poor but acceptable for gait speed and chair stands.
Several additional upper extremity, lower extremity and mixed upper and lower extremity physical performance tests exists. Of these, grip strength probably has the strongest predictive validity for relevant outcomes, including death. Self-reports of behavior change have also been shown to be predictive of subsequent changes in physical functioning, independent of physical performance tests.