An examination of outcome measures for pain and dysfunction in the cervical spine: a factor analysis

Study Design: Cross-sectional design. Objective: To examine and compare the factorial structure of 4 validated neck pain and dysfunction scales. Summary of Background Data: Neck pain and dysfunction is commonly measured using 1 of 4 validated self-reporting questionnaires: the Neck Disability Index (NDI), the Northwick Park Neck Pain Questionnaire (NPQ), the Copenhagen Neck Functional Disability Scale (CNFDS), and the Neck Pain and Disability Scale (NPDS). Although used interchangeably in the literature, recent studies suggest that the 4 scales differ in the number and type of factors that they examine and the weighting of these factors. To date, there have been no direct comparisons made of these scales when applied simultaneously to the same patient population. Methods: Data were collected from 88 patients with mechanical neck pain who completed all 4 questionnaires. Exploratory principal components factor analyses were conducted to expose the underlying factors within each of the scales. Identified factors were examined, characterized, and compared. Results: Factor analysis revealed a single factor for the NDI, 2 factors for the NPQ, and 3 factors for both the CNFDS and NPDS. Factors identified include neck pain, dysfunction related to general activities, neck-specific function, cognition, emotion, and the influence of participation restriction on psychosocial functioning. The 3 NPDS factors appear to assess the multidimensional nature of neck pain and dysfunction most comprehensively. Conclusion: When selecting and interpreting a neck pain and dysfunction scale, clinicians and researchers are encouraged to take into account the factors measured by the NDI, NPQ, CNFDS, and NPDS and their applicability to the specific neck patient population under examination. The decision of which factors are of greatest interest will influence the selection of an appropriate outcome instrument.