Factor analyses for the Orebro Musculoskeletal Pain Questionnaire for working and nonworking patients with chronic low back pain

BACKGROUND CONTEXT: The Orebro Musculoskeletal Pain Questionnaire (OMPQ) has good psychometric properties to predict return to work in patients with acute low back pain. Although it is used in patients with chronic back pain and nonworkers, there is no evidence on the factor structure of the OMPQ in these populations. This is deemed an important prerequisite for future prediction studies. PURPOSE: This study aimed to analyze the factor structure of the OMPQ in working and nonworking patients with chronic back pain. STUDY DESIGN/SETTING: This is a cross-sectional study in a university-based spine center. PATIENT SAMPLE: The patient sample consists two cohorts of working and nonworking adult patients (> 18 years) with specific and nonspecific chronic back pain. OUTCOME MEASURES: The Orebro Musculoskeletal Pain Questionnaire. METHODS: Exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were performed in working (N= 557) and nonworking (N= 266) patients for three, four, five, and six factors identified in literature. A goodness of fit index was calculated by a chi-square. Root mean square error of approximation (RMSEA) was calculated, and the number of factors identified was based on RMSEA values 0.90 are considered to indicate acceptable fit. RESULTS: In working patients, a five-factor solution had the best fit (RMSEA <0.05; NFI and TLI > 0.90), but substantial adaptations should be made to get proper fit (removal of the work-related items). In nonworking patients, a four-factor analysis had the best fit (RMSEA