Assessing Somatic Symptoms With the Patient Health Questionnaire (PHQ-15) in Syrian Refugees.

Somatic symptoms are common among Syrian refugees. To quantify somatic symptom load, sum score models derived from the Patient Health Questionnaire (PHQ-15) have been frequently applied without psychometric justification. Across two studies (total N = 776), we (a) tested different PHQ-15 factor solutions in Syrian refugees, (b) investigated measurement invariance (MI) of the factor solutions compared with German residents, and (c) scrutinized whether sum score models adequately represent the data and differ in associations with external validators compared with factor scores. One-factor, three-factor, four-factor, and a reduced one-factor solution all displayed acceptable to good model fit. The four-factor solution showed the best fit, enabling differential symptom analyses. Sum score models often had poor model fit, necessitating independent investigations before applying them. For all factor solutions, (partial) strict MI between residents and refugees could be established. All scoring methods displayed high and comparable associations with functional impairment, depressive, and anxiety symptoms.