Background: The Beck Depression Inventory, Second Edition (BDI-II), and the Patient Health Questionnaire-9 (PHQ-9) are considered reliable and valid for measuring depressive symptom severity and screening for a depressive disorder. Few studies have examined the convergent or divergent validity of these two measures, and none has been conducted among low-income women-although rates of depression in this group are extremely high. Moreover, variation in within-subject scores suggests that these measures may be less comparable in select subgroups.
Objective: We sought to compare these two measures in terms of construct validity and to examine whether within-subject differences in depressive symptom severity scores could be accounted for by select characteristics in low-income women.
Methods: In a sample of 308 low-income women, construct validity was assessed using a multitrait-monomethod matrix approach, between-instrument differences in continuous symptom severity scores were regressed on select characteristics using backward stepwise selection, and differences in depressive symptom classification were assessed using the Mantel-Haenszel test.
Results: Convergent validity was high (rs = .80, p < .001). Among predictors that included age, race, education, number of chronic health conditions, history of depression, perceived stress, anxiety, and/or the number of generalized symptoms, none explained within-subject differences in depressive symptom scores between the BDI-II and the PHQ-9 (p > .05, R2 < .04). Similarly, there was consistency in depressive symptom classification (χ2 = 172 and 172.6, p < .0001).
Discussion: These findings demonstrate that the BDI-II and the PHQ-9 perform similarly among low-income women in terms of depressive symptom severity measurement and classifying levels of depressive symptoms, and do not vary across subgroups on the basis of select demographics.