Purpose: Major depressive disorder (MDD) negatively impacts different aspects of an individual's life leading to grave impairments in quality of life (QOL). We performed a detailed analysis of the interaction between depressive symptom severity, functioning, and QOL in outpatients with MDD in order to better understand QOL impairments in MDD.
Methods: This cross-sectional study was conducted with 319 consecutive outpatients seeking treatment for DSM-IV-diagnosed MDD at an urban hospital-based outpatient clinic from 2005 to 2008 as part of the Cedars-Sinai Psychiatric Treatment Outcome Registry, a prospective cohort study of clinical, functioning, and patient-reported QOL outcomes in psychiatric disorders using a measurement-based care model. This model utilizes the following measures: (a) Depressive symptom severity: Quick Inventory of Depressive Symptomatology-Self Report (QIDS-SR); (b) Functioning measures: Global Assessment of Functioning (GAF), Sheehan Disability Scale (SDS), Work and Social Adjustment Scale, and the Endicott Work Productivity Scale; and (c) Quality of Life measure: Quality of Life, Enjoyment, and Satisfaction Questionnaire-Short Form (Q-LES-Q).
Results: QOL is significantly impaired in MDD, with a mean Q-LES-Q score for this study population of 39.8 % (SD = 16.9), whereas the community norm average is 78.3 %. Regression modeling suggested that depressive symptom severity, functioning/disability, and age all significantly contributed to QOL. QIDS-SR (measuring depressive symptom severity), GAF, and SDS (measuring functioning/disability) scores accounted for 48.1, 17.4, and 13.3 % (semi-partial correlation values) of the variance in Q-LES-Q, respectively.
Conclusions: Our results show that impairment of QOL increases in a monotonic fashion with depressive symptom severity; however, depression symptom severity only accounted for 48.1 % of the QOL variance in our patient population. Furthermore, QOL is uniquely associated with measures of Functioning. We believe these results demonstrate the need to utilize not only Symptom Severity scales, but also Functioning and Quality of Life measures in MDD assessment, treatment, and research.