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.