Development of the Galaxy Chronic Obstructive Pulmonary Disease (COPD) Model Using Data from ECLIPSE: Internal Validation of a Linked-Equations Cohort Model

Med Decis Making. 2017 May;37(4):469-480. doi: 10.1177/0272989X16653118. Epub 2016 Jun 17.


Background: The recent joint International Society for Pharmacoeconomics and Outcomes Research / Society for Medical Decision Making Modeling Good Research Practices Task Force emphasized the importance of conceptualizing and validating models. We report a new model of chronic obstructive pulmonary disease (COPD) (part of the Galaxy project) founded on a conceptual model, implemented using a novel linked-equation approach, and internally validated.

Methods: An expert panel developed a conceptual model including causal relationships between disease attributes, progression, and final outcomes. Risk equations describing these relationships were estimated using data from the Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints (ECLIPSE) study, with costs estimated from the TOwards a Revolution in COPD Health (TORCH) study. Implementation as a linked-equation model enabled direct estimation of health service costs and quality-adjusted life years (QALYs) for COPD patients over their lifetimes. Internal validation compared 3 years of predicted cohort experience with ECLIPSE results.

Results: At 3 years, the Galaxy COPD model predictions of annual exacerbation rate and annual decline in forced expiratory volume in 1 second fell within the ECLIPSE data confidence limits, although 3-year overall survival was outside the observed confidence limits. Projections of the risk equations over time permitted extrapolation to patient lifetimes. Averaging the predicted cost/QALY outcomes for the different patients within the ECLIPSE cohort gives an estimated lifetime cost of £25,214 (undiscounted)/£20,318 (discounted) and lifetime QALYs of 6.45 (undiscounted/5.24 [discounted]) per ECLIPSE patient.

Conclusions: A new form of model for COPD was conceptualized, implemented, and internally validated, based on a series of linked equations using epidemiological data (ECLIPSE) and cost data (TORCH). This Galaxy model predicts COPD outcomes from treatment effects on disease attributes such as lung function, exacerbations, symptoms, or exercise capacity; further external validation is required.

Keywords: COPD; QALY; cost; model; risk.

Publication types

  • Multicenter Study
  • Observational Study
  • Randomized Controlled Trial

MeSH terms

  • Biomarkers
  • Body Mass Index
  • Bronchodilator Agents / therapeutic use
  • Comorbidity
  • Delphi Technique
  • Disease Progression*
  • Double-Blind Method
  • Health Services / statistics & numerical data
  • Health Status
  • Humans
  • Models, Economic
  • Models, Theoretical*
  • Pulmonary Disease, Chronic Obstructive / economics
  • Pulmonary Disease, Chronic Obstructive / mortality*
  • Pulmonary Disease, Chronic Obstructive / physiopathology*
  • Quality of Life
  • Quality-Adjusted Life Years
  • Respiratory Function Tests
  • Severity of Illness Index
  • Socioeconomic Factors


  • Biomarkers
  • Bronchodilator Agents