Reliability and responsivity of pain intensity scales in individuals with chronic pain.

Prior research supports the validity and short-term test-retest stability of 4 commonly used scales for assessing pain intensity (Visual Analogue Scale [VAS], 6-point Verbal Rating Scale [VRS-6], Numerical Rating Scale [NRS-11], and Face Pain Scale-Revised [FPS-R]). However, the relative stability and ability of these measures to detect changes in pain intensity over longer time periods have not yet been examined, although knowledge regarding these psychometric issues is important for selecting from among these measures. To address this knowledge gap, we administered these scales assessing worst and average pain intensity to 250 chronic pain outpatients on 2 occasions, a little over 6 weeks apart on average. All 4 scales were found to be valid for detecting decreases in pain, and the VAS, NRS-11, and FPS-R evidenced the most validity for detecting increases in pain. The NRS-11 and VAS evidenced better test-retest stability than the VRS-6 and FPS-R. Age affected the ability of the VRS-6 for detecting improvement in worst pain, as well as the ability of the VAS for detecting worsening in both worst and average pain. However, the psychometric properties of the scales were not influenced by education level. Overall, the NRS-11 emerged as showing the most sensitivity and stability. The FPS-R seems to be a good second choice to consider for samples of individuals who might have difficulty understanding or using the NRS-11.