Development of a Japanese version of the Somatic Symptom Scale-8: Psychometric validity and internal consistency

- Japanese version of the Somatic Symptom Scale-8 was psychometrically assessed.
- A strong correlation with anxiety, depression, and health status was observed.
- All except one item were most correlated with their own symptom domain.
- The scale had a good internal consistency.
- The scale is valid, and five severity thresholds are applicable to Japanese.

ObjectiveWe aimed to psychometrically validate the Japanese version of the Somatic Symptom Scale-8 (SSS-8) in Japanese individuals.MethodData were collected from Japanese individuals aged 20-64 years, who were recruited online, in February 2015. The scale reliability and validity were analyzed.ResultsData from 52,353 individuals were analyzed. Cronbach's alpha for the assessment of internal consistency reliability was 0.86 for the total score. The concurrent validity results showed strong correlations with three domains of the Profile of Mood States-Brief form (ρ = 0.51-0.61) and the EuroQol 5 Dimension (ρ = − 0.54). The known-group validity results indicated a linear trend in the severity of depression stratified using the Patient Health Questionnaire-2 (Jonckheere-Terpstra test, p < 0.001). Regarding convergent and discriminant validities, all items correlated most strongly with their own domains (coefficients ≥ 0.5), except for one item (headaches). Scores on perceived stress, pain, and general health differed across five SSS-8 severity groups (Steel-Dwass test, p < 0.001), expect for one group pair in health.ConclusionThe Japanese version of the SSS-8 was valid with good internal consistency. This questionnaire could help detect somatic symptom burdens of chronic and severe musculoskeletal pain for primary prevention.