Agreement between Visual Analog Scale and Numeric Rating Scale in patients with persistent neck pain and is the agreement affected by the own estimated neck function measured with Neck Disability index?

Background: Visual Analog Scale (VAS) and Numeric Rating Scale (NRS) are commonly used for measuring pain intensity. Although several studies have investigated agreement between VAS and NRS, there is a lack of knowledge about agreement in persistent neck pain and whether neck disability affects the agreement. Objective: Evaluate agreement between the two pain rating scales VAS and NRS for patients with persistent neck pain, and evaluate if the agreement is affected by neck disability, measured with Neck Disability Index. Methods: A cohort study with 43 participants with neck pain > 3 months. Neck pain now and average neck pain last week was measured on VAS and NRS, and were recorded two times. Correlation between VAS and NRS was analyzed with Spearmans r and agreement was calculated with Bland Altman. Between group differences in patients with high (>15) compared to low (<15) NDI regarding agreement in VAS/NRS, were analyzed with Mann-Whitney U-test. Results: There was a significant positive correlation between VAS and NRS (r=0,927–r=0,909, p>0,01) and neck disability did not affect the agreement. The largest mean difference was 0,5 with variation between -2 to 2 in 95% of the patients. Conclusion: The same measurement (VAS or NRS) should be used for repeated measuring in neck pain. It is important to be aware of the differences between VAS and NRS, especially when research results will be implemented in primary care