Validity of the numeric rating scale as a measure of dyspnea

Abstract

BACKGROUND: Dyspnea, a devastating sign, is rarely monitored by clinicians. One reason may be the lack of a valid measurement scale that is easy to use in a clinical setting. OBJECTIVES: To establish the validity of the numeric rating scale as a measure of present dyspnea (dyspnea at rest). METHODS: A total of 188 patients with chronic obstructive pulmonary disease rated their present dyspnea by using the Visual Analog Dyspnea Scale and the numeric rating scale. They also rated their usual dyspnea (dyspnea during the past week). Demographic information was collected from each patient's chart, and pulmonary status was assessed with portable spirometry, pulse oximetry, or both. RESULTS: Concurrent validity of the numeric rating scale was supported by the high correlation of its scores with scores from the Visual Analog Dyspnea Scale. Conversion of the numeric rating scale to a 0-to-100 scale and comparison with the visual analog scale (by using a paired t test to determine if the correlated scores were similar for clinical decision making) showed that scores were not significantly different. A paired t test showed a difference in scores on the numeric rating scale obtained before and after ambulation, supporting the construct validity of the numeric rating scale. Scores on the numeric rating scale for present dyspnea were poorly correlated with ratings of usual dyspnea, indicating that present dyspnea and usual dyspnea are different constructs. CONCLUSION: Present and usual dyspnea are different constructs. The numeric rating scale is a valid measure of present dyspnea.