The model employs Monte Carlo simulation methods to follow a patient through the model as dictated by probabilities of developing complications, being symptomatic or progressing, taking into account his, or her, current treatment status. These include the rate of FEV1 decline, the exacerbation rate, the discontinuation rate, and changes in Baseline and Transition Dyspnoea Index (BDITDI) and the St. George’s Respiratory Questionnaire (SGRQ) scores. These clinical events may trigger a treatment switch, which can be specified at the start of the analysis by the user to a maximum of three criteria. For example, the user can specify a treatment switch after the patient has experienced two exacerbations over the course of the last year.