Validation of the patient health questionnaire-9 for major depressive disorder in the occupational health setting

Purpose
Because of the increased risk of long-term sickness leave for employees with a major depressive disorder (MDD), it is important for occupational health professionals to recognize depression in a timely manner. The Patient Health Questionnaire-9 (PHQ-9) has proven to be a reliable and valid instrument for screening MDD, but has not been validated in the occupational health setting. The aim of this study was to validate the PHQ-9 for MDD within a population of employees on sickness leave by using the MINI-International Neuropsychiatric Interview (MINI) as a gold standard.
Methods
Participants were recruited in collaboration with the occupational health service. The study sample consisted of 170 employees on sickness leave between 4 and 26 weeks who completed the PHQ-9 and were evaluated with the MINI by telephone. Sensitivity, specificity, positive and negative predictive value, efficiency and 95 % confidence intervals (95 % CIs) were calculated for all possible cut-off values. A receiver operator characteristics (ROC) analysis was computed for PHQ-9 score versus the MINI. Results The optimal cut-off value of the PHQ-9 was 10. This resulted in a sensitivity of 86.1 % [95 % CI (69.7–94.8)] and a specificity of 78.4 % [95 % CI (70.2–84.8)]. Based on the ROC analysis, the area under the curve for the PHQ-9 was 0.90 [SE = 0.02; 95 % CI (0.85–0.94)].
Conclusion
The PHQ-9 shows good sensitivity and specificity as a screener for MDD within a population of employees on sickness leave.