Rasch validation of the Depression Scale among patients with low back pain

Abstract

BACKGROUND: The Depression Scale (DEPS) is a commonly used screening tool for major depression in studies investigating low back pain, yet it has not been validated for patients with back-specific problems. OBJECTIVE: To assess the psychometric properties of the DEPS in patients with degenerative spinal disease. METHODS: Six hundred and thirty-seven patients with a degenerative spinal disease completed the DEPS instrument. The Rasch Measurement Theory was applied to analyze the measurement properties of the DEPS. The main hypothesis-driven approach was whether the DEPS would meet relevant psychometric criteria for assessing depressive symptoms among patients with degenerative spinal disease. RESULTS: The Mean (SD) DEPS score was 9.2 (6.6). Scale minimum or maximum points among participants were 2.4% and 0.8%, respectively. Cronbach’s alpha for internal consistency was 0.92. Person Separation Index for reliability was 0.88. All items had ordered thresholds and seven of the 10 items had good item fit. Unidimensionality of the DEPS was supported (proportion of significant t-tests, 4.5%). CONCLUSIONS: This study supports the validity of the DEPS for screening depressive symptoms in patients with degenerative spinal disease.