Evaluation of the core outcome measure in whiplash

STUDY DESIGN. Reanalysis of data derived from longitudinal cohort studies. OBJECTIVE. To comprehensively evaluate the psychometric properties of a 5-item version of the Core Outcome Measure in people with whiplash. SUMMARY OF BACKGROUND DATA. The 7-item Core Outcome Measure was initially proposed as a brief health outcome measure for use in low back pain. To date, this measure has not been comprehensively assessed in a whiplash population. METHODS. Data were sourced from 3 separate whiplash cohorts (total 481) encompassing acute, early chronic, and late-chronic whiplash among primary care and insurance populations. Subjects completed a 5-item version of the Core Outcome Measure for whiplash (Core Whiplash Outcome Measure [CWOM]), the Functional Rating Index, Neck Disability Index, SF-36, and perceived recovery questionnaires at baseline and short and long-term follow-up periods. Psychometric evaluation of the CWOM included assessing questionnaire responses, internal consistency, construct validity, and internal and external responsiveness. RESULTS. Internal consistency was excellent at all stages of whiplash (Cronbach α = 0.76 in the acute stage and 0.83 in the late-chronic stage). Convergent validity was observed between the CWOM and Functional Rating Index (Pearson r = 0.81), Neck Disability Index (Pearson r = 0.76), and SF-36 physical health summary measure (Pearson r = -0.65). Divergent validity was observed between the CWOM and SF-36 mental health summary measure (Pearson r = -0.45). The internal and external responsiveness of the CWOM was similar to other neck-specific outcome measures. CONCLUSIONS. We recommend the 5-item CWOM as a brief clinical measure for whiplash because it is quick to administer and score, and has excellent measurement properties. The CWOM may need to be supplemented with other questionnaires (e.g., when assessment of psychological or emotional health is required).