Study design: Cohort study of patients with low back pain (LBP) receiving physical therapy.
Objective: To examine the responsiveness characteristics of the numerical pain rating scale (NPRS) in patients with LBP using a variety of methods.
Summary of background data: Although several studies have assessed the reliability and validity of the NPRS, few studies have characterized its responsiveness in patients with LBP.
Methods: Determination of change on the NPRS during 1 and 4 weeks was examined by calculating mean change, standardized effect size, Guyatt Responsiveness Index, area under a receiver operating characteristic curve, minimum clinically important difference, and minimum detectable change. Change in the NPRS from baseline to the 1 and 4-week follow-up was compared to the average of the patient and therapist's perceived improvement using the 15-point Global Rating of Change scale.
Results: The majority of patients had clinically meaningful improvement after both 1 and 4 weeks of rehabilitation. The standard error of measure was equal to 1.02, corresponding to a minimum detectable change of 2 points. The area under the curve at the 1 and 4-week follow-up was 0.72 (0.62, 0.81) and 0.92 (0.86, 0.97), respectively. The minimum clinically important difference at the 1 and 4-week follow-up corresponded to a change of 2.2 and 1.5 points, respectively.
Conclusions: Clinicians can be confident that a 2-point change on the NPRS represents clinically meaningful change that exceeds the bounds of measurement error.