Explaining heterogeneity in disability with major depressive disorder: effects of personal and environmental characteristics.

BACKGROUND: Major depressive disorder (MDD) is associated with disability, yet some patients function surprisingly well. The reason for this heterogeneity between patients is unclear. Building on the International Classification of Functioning (ICF) model, this study aims to examine effects of personal and environmental characteristics on disability with MDD, over and above illness characteristics.
METHODS: Data were obtained from 573 patients with a current diagnosis of MDD. Three measures for disability were used, varying in objectivity and specificity: 'WHODAS disability', 'days out of role', and 'work absence'. Univariate and stepwise multivariate regression analyses were conducted.
RESULTS: WHODAS disability was best explained by the study variables. Illness characteristics were clearly the strongest correlates of WHODAS disability, whereas personal and environmental characteristics were less influential. Personal and, more restrictedly, environmental characteristics were almost equally important to illness characteristics in explaining days out of role and work absence. High conscientiousness, high neuroticism, low level of physical activity, and high work stress were the strongest predictors of disability among MDD patients. LIMITATIONS: Due to the cross-sectional design of the present study we could not draw conclusions about causal relationships between our predictor variables and disability.
CONCLUSIONS: Personal characteristics appeared to be almost equally important to illness characteristics in explaining heterogeneity in disability when measured objectively and specifically (i.e., days out of role and work absence). However, personal characteristics turned out to be considerably less important to disability measured in a broad and subjective way (i.e., WHODAS disability). Environmental characteristics appeared to have little impact.