Performance-based measures of physical function as mortality predictors: incremental value beyond self-reports

Abstract

Although previous studies have indicated that performance assessments strongly predict future survival, few have evaluated the incremental value in the presence of controls for self-reported activity and mobility limitations. The process linking chronic and acute health conditions to disability has been conceptualized as a progression through four stages: (1) pathology; (2) substantial impairments; (3) functional limitations (restrictions in basic physical or mental performance); and (4) disability (difficulties in various activities of daily life, Verbrugge and Jette 1994). Measures associated with these stages have provided researchers and health professionals with valuable indicators of the current and future health status of community-dwelling populations of older adults. Population-based surveys frequently include measures of the disablement process, either from self-reports or as interviewed-administered performance tests. Although these two types of measures  often labeled ―subjective‖ and ―objective‖ respectively  are statistically correlated, they are thought to capture distinct constructs (Reuben et al. 2004). Nevertheless, both self-reports and performance tasks have been shown to predict subsequent deterioration in health in diverse settings (Bernard et al. 1997; Cooper et al. 2010; Ferrucci et al. 1991; Gill, Robison, and Tinetti 1998; Guralnik et al. 1995; Guralnik et al. 2000; Reuben, Siu, and Kimpau 1992; Tinetti et al. 1995). Each method has advantages and drawbacks. The most frequently used self-reported measures identify: (1) limitations in performing basic activities of daily living (ADL) such as bathing or eating, and (2) mobility limitations such as walking or raising one’s arms. These indicators are easy to collect, inexpensive, and focus on behaviors that are clinically relevant and signal the need for caregiving (Reuben et al. 2004). Although the subjective component of self-reports may capture information of prognostic value, self-reports are likely to be biased by myriad factors (e.g., environmental conditions, cultural preferences, or attitudes) that impede comparisons across populations or subgroups (Melzer et al. 2004) and, given their focus on functional limitations and especially disability, they are unlikely to identify individuals in the early stages of impairment (Reuben et al. 2004). Still, they may be better suited than performance tests to assess individuals’ interactions with their immediate environments and the associated constraints.