Using the Patient Health Questionnaire-9 to measure depression among racially and ethnically diverse primary care patients

OBJECTIVE: The Patient Health Questionnaire depression scale (PHQ-9) is a well-validated, Diagnostic and Statistical Manual of Mental Disorders - Fourth Edition (DSM-IV) criterion-based measure for diagnosing depression, assessing severity and monitoring treatment response. The performance of most depression scales including the PHQ-9, however, has not been rigorously evaluated in different racial/ethnic populations. Therefore, we compared the factor structure of the PHQ-9 between different racial/ethnic groups as well as the rates of endorsement and differential item functioning (DIF) of the 9 items of the PHQ-9. The presence of DIF would indicate that responses to an individual item differ significantly between groups, controlling for the level of depression. MEASUREMENTS: A combined dataset from 2 separate studies of 5,053 primary care patients including non-Hispanic white (n=2,520), African American (n=598), Chinese American (n=941), and Latino (n=974) patients was used for our analysis. Exploratory principal components factor analysis was used to derive the factor structure of the PHQ-9 in each of the 4 racial/ethnic groups. A generalized Mantel-Haenszel statistic was used to test for DIF. RESULTS: One main factor that included all PHQ-9 items was found in each racial/ethnic group with α coefficients ranging from 0.79 to 0.89. Although endorsement rates of individual items were generally similar among the 4 groups, evidence of DIF was found for some items. CONCLUSIONS: Our analyses indicate that in African American, Chinese American, Latino, and non-Hispanic white patient groups the PHQ-9 measures a common concept of depression and can be effective for the detection and monitoring of depression in these diverse populations.