title: Depression as a systemic syndrome: mapping the feedback loops of major depressive disorder.
abstract: BACKGROUND
  Depression is a complex public health problem with considerable variation in treatment response. The systemic complexity of depression, or the feedback processes among diverse drivers of the disorder, contribute to the persistence of depression. This paper extends prior attempts to understand the complex causal feedback mechanisms that underlie depression by presenting the first broad boundary causal loop diagram of depression dynamics.
  
  
  METHODS
  We applied qualitative system dynamics methods to map the broad feedback mechanisms of depression. We used a structured approach to identify candidate causal mechanisms of depression in the literature. We assessed the strength of empirical support for each mechanism and prioritized those with support from validation studies. Through an iterative process, we synthesized the empirical literature and created a conceptual model of major depressive disorder.
  
  
  RESULTS
  The literature review and synthesis resulted in the development of the first causal loop diagram of reinforcing feedback processes of depression. It proposes candidate drivers of illness, or inertial factors, and their temporal functioning, as well as the interactions among drivers of depression. The final causal loop diagram defines 13 key reinforcing feedback loops that involve nine candidate drivers of depression.
  
  
  CONCLUSIONS
  Future research is needed to expand upon this initial model of depression dynamics. Quantitative extensions may result in a better understanding of the systemic syndrome of depression and contribute to personalized methods of evaluation, prevention and intervention.
authors.affiliation: Department of Human Development and Family Studies,Michigan State University,East Lansing,MI,USA.
authors.forename: A K
authors.initials: AK
authors.lastname: Wittenborn
authors.affiliation: Sloan School of Management,Massachusetts Institute of Technology,Cambridge,MA,USA.
authors.forename: H
authors.initials: H
authors.lastname: Rahmandad
authors.affiliation: Department of Human Development and Family Studies,Michigan State University,East Lansing,MI,USA.
authors.forename: J
authors.initials: J
authors.lastname: Rick
authors.affiliation: Department of Industrial and Systems Engineering,Virginia Tech,Blacksburg,VA,USA.
authors.forename: N
authors.initials: N
authors.lastname: Hosseinichimeh
mesh_terms: D003863:Depression / Q000523:psychology*; D003865:Major Depressive Disorder / Q000523:psychology*; D030141:Feedback, Psychological; D006801:Humans; D008960:Models, Psychological; D011634:Public Health
keywords: Feedback loops; feedback mechanisms; major depressive disorder; personalized medicine; system dynamics