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.
Shawn M. Kneipp, PhD, ARNP, is Visiting Associate Professor, Healthcare Environments Division, the University of North Carolina at Chapel Hill School of Nursing; John A. Kairalla, PhD, is Assistant Professor, Division of Biostatistics, Department of Health Outcomes and Policy, College of Medicine; Jeanne Marie R. Stacciarini, PhD, is Assistant Professor, Department of Healthcare Environments and Systems, College of Nursing; Deidre Pereira, PhD, is Assistant Professor, Department of Clinical and Health Psychology, College of Public Health and Health Professions; and M. David Miller, PhD, is Professor, Department of Research Methods and Evaluation, College of Education, University of Florida, Gainesville.
Accepted for publication August 16, 2010.
The authors gratefully acknowledge the women in the Welfare Transition Program who participated in this study, the service providers and administrative personnel in the Florida Works Welfare Transition Program for their ongoing support, and the National Institutes of Health/National Institute of Nursing Research, contract grant number R01NR009406, which supported this research.
Corresponding author: Shawn M. Kneipp, PhD, ARNP, the University of North Carolina at Chapel Hill, School of Nursing, Healthcare Environments Division, Carrington Hall CB#7460, Chapel Hill, NC 27599-7460 (firstname.lastname@example.org).