The committee further discussed the approaches to survival modelling. It noted that the company had challenged the committee's review of the ERG's modelling approach, suggesting that the ERG should have done statistical tests, such as goodness of fit. The committee suggested to the company that, in the single technology appraisal process, the onus is on the company to provide the evidence, including an economic model. It considered that the ERG's role is to critique the evidence, rather than build a new model. The committee heard that the company agreed that this is the case but still considered that the committee should have commented more specifically on the company's supporting statistical tests, which the company considered to provide justification for the use of the gamma distribution to project overall survival. The committee then heard from the ERG that additional statistical tests were not necessary because, in the ERG's opinion, the PARAMOUNT data were sufficiently mature to allow calculation of the survival advantage of pemetrexed without any extrapolation. This was because the trajectories of the pemetrexed and placebo curves were parallel and could be overlaid once overall survival was less than about 37% by shifting the overall survival curve of the control arm to the right by approximately 200 days. This approach allowed the difference in survival to be calculated from the differences in areas under the curves, and was approximately 106 days (3.49 months). The committee understood from the ERG that this approach removed the need to use a hazard function to model the survival data, and was based on a new exploration of data that the company had previously provided, and that had been available throughout the course of the appraisal. After further discussion, the company agreed that there appeared to be no statistically significant difference in post‑progression survival between the trial groups. The committee concluded that extrapolation of the data was not needed and that its decision on the cost effectiveness should be made based on the actual data.