BACKGROUND: More than half of patients with depression go undetected. Self-rating scales can be useful in screening for depression, and measuring severity and treatment outcome. AIM: This study compares the Hospital Anxiety and Depression Scale (HADS) and the Patient Health Questionnaire (PHQ-9) with regard to their psychometric properties, and investigates their agreement at different cut-off scores. METHOD: Swedish primary care patients and psychiatric outpatients (n = 737) who reported symptoms of depression completed the self-rating scales. Data were collected from 2006 to 2007. Analyses with respect to internal consistency, factor analysis, and agreement (Cohen's kappa) at recommended cut-offs were performed. RESULTS: Both scales had high internal consistency (alpha = 0.9) and stable factor structures. Using severity cut-offs, the PHQ-9 (> or =5) diagnosed about 30% more patients than the HADS depression subscale (HADS-D; > or =8). They recognised the same prevalence of mild and moderate depression, but differed in relation to severe depression. When comparing recommended screening cut-offs, HADS-D > or =11 (33.5% of participants) and PHQ-9 > or =10 (65.9%) agreement was low (kappa = 0.35). Using the lower recommended cut-off in the HADS-D (> or =8), agreement with PHQ-9 > or =10 was moderate (kappa = 0.52). The highest agreement (kappa = 0.56) was found comparing HADS-D > or =8 with PHQ-9 > or =12. This also equalised the prevalence of depression found by the scales. CONCLUSION: The HADS and PHQ-9 are both quick and reliable. The HADS has the advantage of evaluating both depression and anxiety, and the PHQ-9 of being strictly based upon the Diagnostic and Statistical Manual of Mental Disorders. The agreement between the scales at the best suitable cut-off is moderate, although the identified prevalence was similar. This indicates that the scales do not fully identify the same cases. This difference needs to be further explored.
Comment In: Br J Gen Pract. 2009 Sep;59(566):636-719761661