Study Design. Prospective study of patients with chronic back pain from lumbar spine disorders.
Objective. To evaluate the degree of interchangeability of a 100-mm visual analog scale (VAS) and a 5-point verbal rating scale (VRS) for the assessment of pain intensity.
Summary of Background Data. The fact that VAS and Likert scales are highly intercorrelated does not mean that both types of scales can be used interchangeably.
Methods. A total of 151 patients (mean age, 52 ± 14.6 years) undergoing elective spine surgery completed a 100-mm VAS and a discrete 5-category VRS corresponding to the first item question of the core set (“How severe was your back pain in the last week?”). Pain intensity on the VAS was rated using the same question than for the VRS. The level of order-consistency (monotonic agreement), disordered pairs (D), percentage of agreement, and systematic disagreement (relative position), and relative concentration ([RC]) were estimated. VAS assessments were transformed into a discrete 5-category, with the cut-off VAS positions being defined by quintiles and equidistantly.
Results. For VAS defined equidistantly, monotonic agreement was 0.840, D was 0.080, and the percentage of identical pairs was 53%. The corresponding figures for VAS defined by quintiles were 0.809, 0.096, and 27.8%. Inconsistencies between the VAS and the VRS scales were also demonstrated by the marginal distributions, with PR values of −0.005 (95% confidence interval [CI], −0.011 to −0.002) and RC values of 0.144 (95% CI, 0.137-0.152) for VAS defined equidistantly, and PR values of 0.391 (95% CI, 0.384-0.397) and RC values of 0.265 (95% CI, 0.255-0.275) for VAS defined by quintiles.
Conclusion. The order-consistency level was low with overlapping of pain records between the 2 scales, indicating that VAS and VRS are not interchangeable and, therefore, a results obtained with the use of each scale cannot be compared.