Rasch measurement properties of the pain medication questionnaire in persons with spinal cord injury

Abstract

Study design: Secondary analysis of cross-sectional population-based self-report data. Objective: To determine how well the Pain Medication Questionnaire (PMQ) measures risk of pain medication misuse and its precision in separating individuals with spinal cord injury (SCI) into meaningful classification categories. Setting: Academic medical center in Southeastern United States. Methods: Data were collected from a population-based registry of SCI (n = 971). Eligible participants included adults with traumatic SCI with residual effects who were at least 1 year post injury and 18 years of age and who had PMQ data in which they reported active use of pain medication at the time of the study (n = 745). Results: Most items (23/26) of the PMQ contributed to a single unidimensional construct. Rasch analysis results revealed that the rating scale, majority of persons (>93%), and majority of items (20/23) fit the Rasch measurement model. The PMQ demonstrated adequate reliability (person reliability = 0.67) and separated persons into two strata—those likely to misuse pain medication and those with low liklihood of misusing pain medication. Conclusions: Findings offer a deeper understanding of the measurement properties of the PMQ as a precursor for widespread population-based studies to elucidate the incidence of pain medication misuse in persons with SCI. Results also have important research and clinical implications for commonly used PMQ total score cut-offs, which may misclassify an individual’s risk of pain medication misuse.