Fig. 4

Scatter plot of incremental total population costs against incremental total population quality-adjusted life year (QALYs) in Strategy 2 (alternative) compared to Strategy 1 (reference). Strategy 1 consists of five available non-steroidal anti-inflammatory drugs (NSAIDs) and Strategy 2 consists of the same available NSAIDs as in Strategy1 and two tumour necrosis factor-α antagonists. The clouds corresponding to January 1 of 2019, 2024, 2029 and 2034 were obtained from simulations with four different time spans of decision, 5, 10, 15 and 20 years, respectively. In each cloud, each data point was obtained from one run of simulation for all the AS patients appearing in the period from January 1, 2014 to the end of the corresponding time span with a set of model parameter values sampled from appropriate probability distributions; 10,000 runs were executed which resulted in 10,000 data points. All the data points in the four clouds lie in the north-east quadrant of the plane