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

Aims and method To explore the modern psychometric properties of the Patient Health Questionnaire (PHQ-9), we used the Rasch analysis in a sample of 767 primary care patients with depression. Results The analysis highlighted dependency issues between items 1 and 2 ('Little interest or pleasure in doing things' and 'Feeling down, depressed, or hopeless'), and items 3 and 4 ('Trouble falling or staying asleep, or sleeping too much' and 'Feeling tired or having little energy'). Items 1 and 2 displayed an over-discrimination, suggesting their potential redundancy 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 potentially redundant items to deliver a stable screening tool. The results also lend support for the PHQ-2 to be used as a screening tool in a primary care setting.