Development and Validation of the Somatic Symptom Disorder-B Criteria Scale (SSD-12).

Objective: To develop and validate a new self-report questionnaire for the assessment of the psychological features of Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition somatic symptom disorder.

Methods: The Somatic Symptom Disorder-B Criteria Scale (SSD-12) was developed in several steps from an initial pool of 98 items. The SSD-12 is composed of 12 items; each of the three psychological subcriteria is measured by four items. In a cross-sectional study, the SSD-12 was administered to 698 patients (65.8% female, mean [standard deviation] age = 38.79 [14.15] years) from a psychosomatic outpatient clinic. 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 α = .95). Confirmatory factor analyses suggested that a three-factorial structure that reflects the three psychological criteria interpreted as cognitive, affective, and behavioral aspects (n = 663, Comparative Fit Index > 0.99, Tucker-Lewis Index > 0.99, Root Mean Square Error of Approximation = 0.06, 90% confidence interval = 0.01-0.08). SSD-12 total sum score was significantly associated with somatic symptom burden (r = 0.47, p < .001) and health anxiety (r = 0.71, p < .001), and moderately associated with general anxiety (r = 0.35, p < .001) and depressive symptoms (r = 0.22, p < .001). Patients with a higher SSD-12 psychological symptom burden reported higher general physical and mental health impairment and significantly higher health care use.

Conclusions: The SSD-12 is the first self-report questionnaire that operationalizes the new psychological characteristics of Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition somatic symptom disorder. Initial assessment indicates that the SSD-12 has sufficient reliability and validity to warrant further testing in both research and clinical settings.