Other: Confirmatory factor analysis of the verbal rating scale on the McGill pain questionnaire short form

Abstract

Previous research has examined the factor structure of the McGill Pain Questionnaire- Short Form (MPQ-SF). Results have varied, but have supported the notion that the verbal descriptors of the MPQ-SF assess two constructs: Affective and Sensory pain. The present study examined the fit of a commonly reported three factor model. Two factors consisting of “Sensory” and “Affective” pain related words were modeled as belonging to a third, higher order factor of “Pain”. The sample consisted of 1185 patients reporting to two multidisciplinary pain treatment centers in a large Midwestern U.S. city. The combined sample's demographic information represented a wide range of disorders (34% myofascial pain, 38% low back pain), pain chronicity (range: 1 – 591 months), ages (range 12–91 years), education levels (6–21 years), and ethnicity (18% African American, 76% Caucasion). Confirmatory factor analytic procedures were conducted on the Verbal Rating Scale of the MPQ-SF using a combined sample of adequate “goodness of fit” indices were obtained by this model: GFI = .84, AGFI = .90, PGFI = .62. A higher than expected Root Mean Square Error of Approximation (RMSEA = .11) indicates a need for continued model evaluation. Alternative models are suggested, and implications of demographic differences and differential item functioning are offered. Proposals for psychometric calibration of items using Item Response Theory are discussed.