Categorising the severity of neck pain: Establishment of cut-points for use in clinical and epidemiological research

Grading pain intensity scales into simple categories provides useful information for both clinicians and epidemiologists and methods to classify pain severity for numerical rating scales have been recommended. However, the establishment of cut-points is still in its infancy and little is known as to whether cut-points are affected by age or gender. The objectives of this paper were to establish optimal cut-points in pain severity in individuals with neck pain (NP) and to investigate if the cut-points were influenced by gender, age, and NP duration. Data from the population-based `Funen Neck and Chest Pain Study' was used. Univariate and multivariate analyses of variance were performed to calculate optimal single and double cut-points for three different pain intensity scores within the past 2 weeks relative to two neck disability scales (`global assessment of NP' and the `Copenhagen Neck Functional Disability Scale'). The two disability scales showed small differences in optimal cut-points. Furthermore, cut-points changed for each of the three pain intensity scales. Only small gender differences in cut-points were seen and no specific trend was noted in either single or double cut-points in different age groups. The cut-points were almost identical for acute, subacute, and chronic NP. This paper has implications for understanding the impact of using different pain intensity scales and provides reference cut-points in NP for use in future clinical and epidemiological research.