title: Disability in major depression related to self-rated and objectively-measured cognitive deficits: a preliminary study.
abstract: BACKGROUND
  Although major depression (MD) is associated with high levels of disability, the relationships between cognitive dysfunction and self-rated disability are poorly understood. This study examined the relationships between self-rated disability in persons with MD and both self-rated and objectively-measured cognitive functioning.
  
  
  METHODS
  Twenty-one persons with MD and 21 control participants underwent neuropsychological assessment and z-scores representing deviations from control performance were calculated and averaged across the domains of psychomotor speed, initial learning, memory retention and executive function. Self-ratings of cognitive deficits (SRCDs) were reported on a 6-point scale for overall rating of cognitive change, speed of thinking, concentration, and short-term memory. Disability scores for self-rated physical, mental-health and functional (ie. days out of role) disability were computed from the Brief-Disability Questionnaire and the SF-12 'mental component' subscale.
  
  
  RESULTS
  Persons with MD had a mean age of 53.9 years (SD = 11.0, 76% female) and had moderate to high depression severity (mean HDRS 21.7, sd = 4.4). As expected, depression severity was a strong predictor of physical (r = 0.7, p < 0.01), mental-health (r = 0.7, p < 0.01) and functional (r = 0.8, p < 0.001) disability on the Brief Disability Questionnaire. Additionally, for physical disability, both overall SRCDs and objectively-measured psychomotor speed continued to be independent significant predictors after controlling for depression severity, uniquely accounting for 13% and 16% of variance respectively. For functional disability scores, objectively-measured memory impairment and overall SRCDs were no longer significant predictors after controlling for depression severity.
  
  
  CONCLUSIONS
  While depression severity is associated with disability, the contributions of both self-rated and objectively-measured cognitive deficits are substantial and contribute uniquely and differentially to various forms of disability. Efforts directed at reducing cognitive deficits in depression may have the potential to reduce disability.
authors.affiliation: Brain & Mind Research Institute, University of Sydney, Camperdown, Australia. snaismith@med.usyd.edu.au
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Naismith
authors.forename: Wendy A
authors.initials: WA
authors.lastname: Longley
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Scott
authors.forename: Ian B
authors.initials: IB
authors.lastname: Hickie
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D003072:Cognition Disorders / Q000145:classification / Q000209:etiology*; D003865:Major Depressive Disorder / Q000150:complications* / Q000523:psychology*; D006233:Persons with Disabilities / Q000523:psychology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012647:Self-Assessment; D012720:Severity of Illness Index