Psychometric validation of the German version of the somatic symptom disorder - B criteria scale (SSD-12) in a primary care population with depression and anxiety: A COSMIN-guided analysis
Abstract
OBJECTIVE: Somatic Symptom Disorder (SSD) is common and often underdiagnosed in primary care, especially in patients with depression and anxiety. The SSD-12 is a self-report questionnaire assessing psychological features of SSD. This study aimed to validate the SSD-12 longitudinally in a primary care sample with depressive and/or anxiety symptoms, following COSMIN guidelines.
METHODS: We conducted a secondary analysis of the PROVIDE-C trial, including 365 adults with moderate depressive and/or anxiety symptoms. Psychometric evaluation of the SSD-12 used data from three time points (baseline, 6, and 12 months). Factorial validity was assessed via confirmatory factor analysis (CFA) comparing unidimensional and three-factor models. Measurement invariance was examined across gender, age, chronic illness, and study arms using multi-group and longitudinal CFA. Additional analyses included internal consistency (McDonald's Omega), test-retest reliability (ICC), measurement error (SEM, SDC), convergent validity (correlations with PHQ-9, GAD-7, RAS-G, SF-12, EQ-5D), and responsiveness (correlations of SSD-12 change scores with PHQ-ADS change).
RESULTS: CFA supported a three-factor structure (cognitive, affective, behavioral) at all time points. Measurement invariance was confirmed across subgroups and longitudinally. The SSD-12 showed high internal consistency, adequate test-retest reliability, and good responsiveness. Construct validity showed moderate positive correlations with…
How strong is the evidence?
Evidence Hub reads this as a cross-sectional, done in people. Its evidence level is 4 of 5 (Low · observational). Observational designs can show an association but not prove cause. Reported size: 365 participants or records.
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