Comparison of two self-rating scales to detect depression: HADS and PHQ-9.
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.