Fig. 1

a Final conceptual model of COPD. b Linked-equations disease progression model for COPD. 6MWT 6-min walk test, COPD chronic obstructive pulmonary disease, EQ-5D EuroQol 5 dimension, FEV1 forced expiratory volume in 1 s, FEV1%p forced expiratory volume in 1 s percent predicted, HRQoL health-related quality of life, QALY quality-adjusted life year, SGRQ St. George’s Respiratory Questionnaire. a Adopted from Tabberer et al. [15]. b Adapted from Briggs et al. [14]. a Figure represents association between baseline covariates, intermediate outcomes (FEV1, symptoms, exacerbations and 6MWT) and final outcomes (mortality, HRQoL and costs). Arrows represent direction of effect e.g. baseline covariates affect intermediate outcomes. b Figure represents schema of linked equations model. Baseline covariates at t = 0 predict intermediate and final outcomes at t = 1 (model cycle = 1). These then become baseline covariates t = 1 to predict intermediate and final outcomes at t = 2 (model cycle = 2)