When examining the published literature on the cost effectiveness of COPD treatments, the majority of studies identified perform pharmacoeconomic evaluations alongside clinical trials, using effectiveness and cost data collected prospectively over the course of the trial In a systematic review published in 2008, ten out of the 15 studies identified were evaluations alongside clinical trials and five were based on economic models . While randomized controlled trials (RCTs) are considered the gold standard for the evaluation of clinical efficacy , the generalizability of an economic evaluation alongside an RCT to real-life clinical practice may be limited due to the choice of comparator and the availability of data over a long period of time (i.e. study duration). Buxton et al. discuss the limitations of trial -based evaluation versus the dangers of modeling but acknowledge that models allow for the extrapolation of data when only short-term data exist, the linking of intermediate trial endpoints to long-term outcomes of interest to the payer, making adjustment to make the evaluation more generalizable to other settings, and the incorporation of other comparator data not included in trials. Economic models are useful alternatives when RCTs do not provide all the information necessary; however, models should endeavour to be as simple as possible while still meeting the stated objective.