Somatic symptoms in the general population of Spain: Validation and normative data of the Patient Health Questionnaire-15 (PHQ-15)

Objective: The Patient Health Questionnaire (PHQ-15) has been widely used to assess somatic symptoms. This study aimed to analyze the psychometric properties of the Spanish version of the PHQ-15, its structure and score distribution across demographic variables in a Spanish sample. In addition, we examined variations in somatic symptoms among different demographic subgroups. Method: 1495 individuals from the Spanish population answered a series of self-reported measures, including PHQ-15. To examine the factorial structure of the PHQ-15, Confirmatory Factor Analysis (CFA) was performed. Additionally, a bifactor CFA model was examined using the Exploratory Structural Equation Modeling (ESEM) framework. Results: Women showed more somatic symptoms than men, and younger individuals showed more somatic symptoms than the older ones. It was also revealed positive associations between somatic symptoms and levels of depression, anxiety, and suspiciousness, while negative associations were found between somatic symptoms and perceived resilience and happiness. Regarding the factorial structure of the PHQ-15, although the one-factor and bifactor models were suitable, the bifactor model underscores the presence of a robust general factor. Limitations: It is a cross-sectional study, not including non-institutionalized individuals. Conclusion: Somatic symptoms are more frequent in women and younger individuals. Furthermore, the presence of physical symptoms is associated to other psychological aspects, such as depression or anxiety. Finally, bifactor model was the most appropriate to explain the factorial structure of the PHQ-15.