Screening for depression in primary care: A Rasch analysis of the PHQ-9

Aims and method: To explore the modern psychometric properties of the PHQ-9. Method: We used RASCH analysis to investigate the psychometric properties of the PHQ-9in a sample of 767 primary-care patients with depression. Results: The analysis highlighted dependency issues between items 1 & 2 (“Little interest or pleasure in doing things” & “Feeling down, depressed, or hopeless”), and items 3 & 4 (“Trouble falling or staying asleep, sleeping too much” & “Feeling tired, having little energy”). Items 1 & 2 displayed an over-discrimination, suggesting potential redundancy of these items within the complete item set. Clinical Implications: In its current format the PHQ-9 displays some problems with regard to its measurement structure among a sample of primary-care patients. These problems can be addressed by removing potential redundant items to deliver a stable screening tool. The results also lend support for the PHQ-2 to be used as a screening tool within a primary-care setting.