Screening for anxiety and depression: validation of the Patient Health Questionnaire for Depression and Anxiety (PHQ-4) in a large sample of rehabilitation patients

PURPOSE: Anxiety and depression are the most prevalent mental disorders in rehabilitation populations and negatively impact rehabilitation outcomes. The Patient Health Questionnaire for Depression and Anxiety (PHQ-4) is an ultra-brief screening instrument validated for general and primary care populations. We validated the PHQ-4 for the first time for the rehabilitation setting. MATERIALS AND METHODS: The study sample consisted of 66,412 patients attending multimodal inpatient rehabilitation, covering various medical indications. To validate the PHQ-4's factorial validity, we conducted confirmatory factor analyses (CFA). Multi-group CFAs assessed measurement invariance. Convergent validity was tested using ordinal logistic regression to model the PHQ-4's association with measures of quality of life, vocational impairment, and work ability. RESULTS: The results demonstrated excellent fit for a two-factor solution. Reliability indices were adequate for a screening instrument (McDonald's ω .775-.852). Measurement invariance was demonstrated across age, gender, and all but one medical indication. Convergent validity was supported, showing associations with age and common patient reported outcomes. CONCLUSIONS: This study demonstrates that the PHQ-4 is a valid and reliable tool for screening for anxiety and depression in rehabilitation settings. Based on a substantial sample and preregistered analysis strategy, the findings will likely generalize to rehabilitation populations in other countries.