Latent structure and factor invariance of somatic symptoms in the patient health questionnaire (PHQ-15).

Abstract Background Somatic symptoms are highly prevalent in primary care although insufficiently understood. The Patient Health Questionnaire (PHQ-15) is a valuable screening test but it has not yet been possible to unequivocally demonstrate its latent structure and measurement invariance. Methods A total of 1,255 patients from 28 primary care centres suffering symptoms of anxiety, depression or somatisation participated in a clinical trial. They completed the PHQ-15 at baseline and 374 retook it at three months. Exploratory structural equation modelling (ESEM) was used to compare three models: 1) a single global factor for somatisation, 2) four specific correlated factors, and 3) a bifact…