Factor structure and longitudinal measurement invariance of PHQ-9 for specialist mental health care patients with persistent major depressive disorder: Exploratory Structural Equation Modelling

Guo, Boliang; Kaylor-Hughes, Catherine; Garland, Anne; Nixon, Neil; Sweeney, Tim; Simpson, Sandra; Dalgleish, Tim; Ramana, Rajini; Yang, Min; Morriss, Richard

Abstract

Background: The Patient Health Questionnaire-9 (PHQ-9) is a widely used instrument for measuring levels of depression in patients in clinical practice and academic research; its factor structure has been investigated in various samples, with limited evidence of measurement equivalence/invariance (ME/I) but not in patients with more severe depression of long duration. This study aims to explore the factor structure of the PHQ-9 and the ME/I between treatment groups over time for these patients.
Methods: 187 secondary care patients with persistent major depressive disorder (PMDD) were recruited to a randomised controlled trial (RCT) with allocation to either a specialist depression team arm or a general mental health arm; their PHQ-9 score was measured at baseline, 3, 6, 9 and 12 months. Exploratory Structural Equational Modelling (ESEM) was performed to examine the factor structure for this specific patient group. ME/I between treatment arm at and across follow-up time were further explored by means of multiple-group ESEM approach using the best-fitted factor structure.
Results: A two-factor structure was evidenced (somatic and affective factor). This two-factor structure had strong factorial invariance between the treatment groups at and across follow up times.
Limitations: Participants were largely white British in a RCT with 40% attrition potentially limiting the study’s generalisability. Not all two-factor modelling criteria were met at every time-point.
Conclusion: PHQ-9 has a two-factor structure for PMDD patients, with strong measurement invariance between treatment groups at and across follow-up time, demonstrating its validity for RCTs and prospective longitudinal studies in chronic moderate to severe depression.

• Journal Article Type: Article
• Acceptance Date: May 6, 2017
• Online Publication Date: May 8, 2017
• Publication Date: 2017-09
• Deposit Date: May 10, 2017
• Publicly Available Date: May 10, 2017
• Journal: Journal of Affective Disorders
• Print ISSN: 0165-0327
• Electronic ISSN: 1573-2517
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 219
• Pages: 1-8
• DOI: https://doi.org/10.1016/j.jad.2017.05.020
• Keywords: PHQ-9, factor structure, measurement equivalence/invariance, Exploratory Structural Equational Modelling, major depressive disorder, chronic depression
• Public URL: https://nottingham-repository.worktribe.com/output/885602
• Publisher URL: http://www.sciencedirect.com/science/article/pii/S0165032716317852
• Additional Information: This article is maintained by: Elsevier; Article Title: Factor structure and longitudinal measurement invariance of PHQ-9 for specialist mental health care patients with persistent major depressive disorder: Exploratory Structural Equation Modelling; Journal Title: Journal of Affective Disorders; CrossRef DOI link to publisher maintained version: https://doi.org/10.1016/j.jad.2017.05.020; Content Type: article; Copyright: © 2017 Elsevier B.V. All rights reserved.