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The Visual Analog Scale and a Five-Item Verbal Rating Scale Are Not Interchangeable for Back Pain Assessment in Lumbar Spine Disorders

Matamalas, Antònia MD*; Ramírez, Manuel MD*; Mojal, Sergi Licentiate in Biostatistics†; De Frutos, Ana García MD*; Molina, Antonio MD, PhD*; Saló, Guillem MD, PhD*; Lladó, Andreu MD, PhD*; Cáceres, Enric MD, PhD*

doi: 10.1097/BRS.0b013e3181e7b315
Health Services Research

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.

Data obtained in 151 patients with chronic back pain from lumbar spine disorders undergoing elective spine surgery show that a 100-mm visual analog scale and a 5-point Likert verbal rating scale, although both valid and reliable, cannot be used interchangeably for the assessment of pain intensity.

From the *Service of Orthopaedic Surgery and Traumatology, Hospital Universitario del Mar, Universitat Autònoma de Barcelona, Barcelona, Spain; and †Service of Methodological Consulting in Biomedical Research, Institut Municipal d'Investigació Mèdica (IMIM-Hospital del Mar), Barcelona, Spain.

Acknowledgment date: February 24, 2009. First revision date: June 26, 2009. Second revision date: March 8, 2010. Acceptance date: March 12, 2010.

Presented as an oral communication at: The 9th Congress of the European Federation of National Associations of Orthopaedics and Traumatology (EFORT), Nice, France. 29 May-1 June, 2008.

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Manuel Ramírez, MD, Service of Orthopaedic Surgery and Traumatology, Hospital Universitario del Mar, Universitat Autònoma de Barcelona, Passeig Marítim 25-29, E-08003 Barcelona, Spain; E-mail: mramirez@imas.imim.es

© 2010 Lippincott Williams & Wilkins, Inc.