The evaluation of change in pain intensity: a comparison of the P4 and single-item numeric pain rating scales

Prospective observation study. To compare the test-retest reliability and longitudinal validity (sensitivity to change) of 2 single-item numeric pain rating scales (NPRSs) with a 4-item pain intensity measure (P4). Pain is a frequent outcome measure for patients seen in physical therapy; however, the error associated with efficient pain measures, such as the single-item NPRS, is greater than for self-report measures of functional status. Initial evaluation of the P4 suggests that it is more reliable and sensitive to change than the NPRS. Two single-item NPRSs and the P4 were administered on 3 occasions--initial visit (n = 220), within 72 hours of baseline (n = 213), and 12 days following baseline assessment (n = 183)--to patients with musculoskeletal problems receiving physical therapy. Reliability was assessed using a type 2,1 intraclass correlation coefficient. Longitudinal validity was assessed by correlating the measures' change scores with a retrospective rating of change that included patients' and clinicians' perspectives. The test-retest reliability and longitudinal validity of the P4 were significantly greater (P1