Aim: The Somatic Symptom Disorder-B Criteria Scale (SSD-12) assesses the psychological features of DSM-5 somatic symptom disorder. The purpose of the current study was to investigate the psychometric characteristics and validity of the 12-item instrument to demonstrate its suitability in primary care.
Method: The study was designed as a cross-sectional survey set in five primary care practices from Munich, Germany (n = 501, 52.0% female, mean age 47 ± 16 years). Item and scale characteristics, as well as measures of reliability and validity, were determined.
Results: The SSD-12 has good item characteristics and excellent reliability (Cronbach's α = 0.92). Confirmatory factor analyses provided evidence to support a general factor model of the SSD-12 in primary care (comparative fit index > 0.98, Tucker-Lewis index > 0.98, root mean square error of approximation = 0.090, 90% confidence interval: 0.078-0.102). SSD-12 total sum-score was significantly associated with somatic symptom burden (r = 0.48, P < 0.001), general anxiety (r = 0.54, P < 0.001) and depressive symptoms (r = 0.60, P < 0.001). At the group level, SSD-12 scores could differentiate between different patient groups (e.g. with and without chronic illness).
Conclusions: The SSD-12 appears to be a reliable, valid and time-efficient self-report measure of the psychological characteristics related to the experience of somatic symptoms which is suitable for primary care. Future research should evaluate its responsiveness to treatment and feasibility as a screening tool in different clinical settings.