Psychosomatic symptoms questionnaire (PSQ-39): a psychometric study among general population of Iranian adults

BACKGROUND: Psychosomatic symptoms, characterized by physical-bodily complaints not fully explained by organic reasons, are highly prevalent. The present study aimed to culturally adapt and evaluate the psychometric properties of Psychosomatic Symptoms Questionnaire 39-item version (PSQ-39) among Iranian general adult population. METHODS: This study included 996 Persian-speaking people, living in Isfahan, Iran. The translation of the PSQ-39 was performed using the forward-backward method. Test-retest reliability was evaluated through Intraclass correlation (ICC) coefficient and internal consistency by using Cronbach’s α. Construct validity was investigated by using both exploratory (EFA) and confirmatory (CFA) factor analysis. Short Form Health Survey (SF-36) was used to assess divergent validity. Known-group validity was also assessed. RESULTS: The Persian version of the PSQ-39 showed excellent test-retest reliability in all domains (ICCs: 0.95–0.99). The computed Cronbach’s alpha coefficients for domains of PSQ-39 were in the range good to excellent. The PSQ-39 showed good known-group validity and differentiated patients from the general population (Area under the curve [AUC] of 0.78 (95% CI: 0.73, 0.84). Construct validity evaluated by EFA led to extraction of seven factors (Cardiorespiratory, musculoskeletal, psychological, gastrointestinal, general, body balance and Globus), and the CFA confirmed the adequacy of extracted factors by EFA (CFI = 0.91, TLI = 0.90, PCFI = 0.77, PNFI = 0.71, CMIN = 1413.18 (df = 654), CMIN/DF = 2.16, and RMSEA = 0.06). Significant negative correlations between all domains of PSQ and SF-36 revealed an acceptable divergent Validity. CONCLUSIONS: The Persian version of the PSQ-39 is a reliable and valid questionnaire with applicability in a broad range of Persian language populations for assessing common psychosomatic symptoms in research as well as in clinical practice. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12888-021-03278-z.