, that is, a treatment switch or
re-initiation of therapy for a patient who has discontinued therapy without the addition of more health states to describe what should be a similar clinical pathway but with slightly different risks of clinical events occurring. Moreover, designing a model with more complex treatment pathways may encounter a lack of appropriate data on transition probabilities between health states and costs. Defining health states based on GOLD criteria is also often problematic as several clinical studies base their endpoint measurements on pre-bronchodilator measurements, rather than post-bronchodilator measurements as prescribed by GOLD once past the screening stage; this limits the applicability of these data in a model.