Comment on: Modelling the cost effectiveness of TNF antagonists in the management of rheumatoid arthritis: results from the British Society for Rheumatology Biologics Registry.

SIR, We thank Dr Von Vollenhoven for his interest in our paper. The questions [1] he raises about our article that examined the cost–effectiveness of biologics using the British Society for Rheumatology Biologics Registry (BSRBR) [2] provide an excellent opportunity to describe why decision modelling should be used in calculating a majority of cost–effectiveness ratios. We refer to an article by Sculpher et al. [3], which eloquently explains many of these points in detail. It should be noted that while the title of the paper refers to trials, much of its content is applicable to a registry like the BSRBR. We summarize the key points: