Assessing functional impairment in a working military population: the Walter Reed functional impairment scale.

Measurement of functional impairment is a priority for the military and other professional work groups routinely exposed to stressful traumatic events as part of their occupation. Standard measures of impairment used in general or chronically ill populations contain many items not suitable for these populations, and include mental health symptoms items that are not true measures of functioning. We created a new, 14-item scale-the Walter Reed Functional Impairment Scale-to assess functioning in 4 domains (physical, occupational, social, and personal). We asked 3,380 soldiers how much difficulty they currently have in each of the 4 domains on a 5-point scale. Behaviorally based psychosocial and occupational performance measures and general health questions were used to validate the scale. The utility of the scale was assessed against clinical measures of psychopathology and physical health (depression, posttraumatic stress disorder [PTSD], general health, generalized physical symptoms). We utilized Cronbach's alpha, item response theory, and the score test for trend to establish consistency of items and the validity of the scale. The scale exhibited excellent reliability (Cronbach's α= 0.92) and validity. The individual items and quartiles of sum scores were strongly correlated with negative occupational and social performance, and the utility of the scale was demonstrated by strong correlations with depression, PTSD, and high levels of generalized physical symptoms. This scale exhibits excellent psychometric properties in this sample of U.S. soldiers and, pending future research, is likely to have utility for other healthy occupational groups.