Psychometric evaluation of the somatic symptom scale − 8 in patients with somatic symptom disorder in Iran

Somatic symptoms are central to many medical diseases and are crucial for evaluating the severity and progression of illness. The Somatic Symptom Scale (SSS-8) was developed as a concise, patient-reported measure of somatic symptom burden. This study aimed to enrich the literature on the SSS-8 by evaluating the psychometric properties of the Persian adaptation of the SSS-8 in patients diagnosed with somatic symptom disorder (SSD) in Iran. A purposive sampling method was used to select 120 SSD patients aged 18 to 60 years old (M = 36.52, SD = 11.39; 75.8% women) from various psychosomatic outpatient clinics in Tehran. Confirmatory factor analyses supported both a simple general-factor model and a higher-order general-factor model of the SSS-8. Cronbach’s alpha and test-retest analysis over a two-week period confirmed the SSS-8’s reliability. The SSS-8 scores also showed the expected correlations with theoretically relevant external correlates, supporting its convergent validity. Finally, the optimal cut-off score for diagnosis was identified as greater than 8, with a sensitivity of 81.82% and a specificity of 58.58%. Overall, the Persian SSS-8 demonstrated robust psychometric properties in individuals with SSD in psychosomatic settings. Its simplicity and efficiency make it a valuable tool for the early and primary diagnosis of SSD, offering a quick and effective means of evaluation, especially in busy primary care settings, for evaluating a range of patient symptoms, including those related to the stomach, bowel, pain, and dizziness, while also assessing symptom severity.