title: A markov model approach assessing the cost of illness of generalized anxiety disorder in Canada.
abstract: BACKGROUND
  Generalized anxiety disorder (GAD) is a chronic disease with waxing and waning of symptoms. This is the first comprehensive economic model developed to reflect the nature and course of GAD.
  
  
  METHODS
  An incidence-based probabilistic Markov model was developed reflecting nine GAD health states (HS): clinical assessments (three HS), maintenance therapies (four HS), discontinuation (one HS), and death (one HS). A probability curve of the GAD onset (ages 18-80) determined entry into the model and assumed patients retained the diagnoses until death. Canadian Psychiatric Association (CPA) guidelines determined pharmacotherapy, with revisions/validation by an expert panel. Direct costs (clinician, pharmacotherapy, hospitalization) were retrieved from government publications. Remission was based on pooled-analysis of CPA-cited evidence. Remaining clinical rates, absenteeism, and hospitalization were retrieved from the literature. Direct costs were attributed throughout the model except for the discontinuation and death HS. Indirect costs (wage rate) were retrieved from government publications and the literature (absenteeism), and were attributed to patients with GAD ≤65 years of age. Results were discounted at 5% and results expressed in 2008 Canadian dollars.
  
  
  RESULTS
  The mean lifetime cost of illness (COI) was estimated to be $31,213 (SD $9,100) per patient. The cost of absenteeism accounted for 96% of the mean COI. The mean age of onset was 31 years and approximately 19% did not respond to pharmacotherapy. Over 85% of patients discontinued treatment by the fourth cycle (2nd year of therapy). Over the course of the model, a mean of 53% of patients relapsed, with an average rate of 0.79 relapses per patient. On average and over a lifetime, the disorder went unmanaged over a period of 14 (SD 9) years. The model was most sensitive to absenteeism.
  
  
  CONCLUSIONS
  GAD is a costly disease with a lifetime COI <$32k/patient, with absenteeism exerting a significant impact.
authors.affiliation: Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College Street, Toronto, ON M5S 3M2 Canada.
authors.forename: Basil G
authors.initials: BG
authors.lastname: Bereza
authors.affiliation: Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College Street, Toronto, ON M5S 3M2 Canada ; Toronto Health Technology Assessment Collaborative, University of Toronto, Toronto, ON Canada.
authors.forename: Márcio
authors.initials: M
authors.lastname: Machado
authors.affiliation: Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College Street, Toronto, ON M5S 3M2 Canada ; Eli Lilly Canada Inc., 3650 Danforth Avenue, Toronto, ON M1N 2E8 Canada.
authors.forename: Manny
authors.initials: M
authors.lastname: Papadimitropoulos
authors.affiliation: Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College Street, Toronto, ON M5S 3M2 Canada ; Centre for Addiction and Mental Health, 250 College Street, Toronto, ON M5T 1R8 Canada.
authors.forename: Beth
authors.initials: B
authors.lastname: Sproule
authors.affiliation: Centre for Addiction and Mental Health, 250 College Street, Toronto, ON M5T 1R8 Canada ; Department of Psychiatry, University of Toronto, 33 Russell Street, Toronto, ON M5S 2S1 Canada.
authors.forename: Arun V
authors.initials: AV
authors.lastname: Ravindran
authors.affiliation: Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College Street, Toronto, ON M5S 3M2 Canada.
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Einarson
keywords: Absenteeism; Cost of illness; Decision model; Economics; Generalized anxiety; Markov model; Pharmacotherapy