Analyses
The analyses of lifestyle, metformin, and placebo were based on the design, cost, and clinical effectiveness of the interventions as implemented in the 3 years of the DPP and the 7 years of the DPPOS. For the DPP group lifestyle sensitivity analysis, we estimated what the costs of lifestyle would have been during the 3 years of DPP if the 16-session core curriculum and monthly follow-up visits with the casemanagers had been conducted as group sessions with 10 participants. We further assumed that outcomes would have been the same as observed for lifestyle. We excluded from the analyses the costs of the research component of the DPP/DPPOS. All costs were expressed as year 2010 U.S. dollars (Supplementary Table 2). Analyses were performed with a 10-year time horizon. Initial analyses were performed without adjusting for survival or discounting. Subsequently, both cost and health outcomes were adjusted for survival and converted to net present value using a 3% discount rate, and incremental costeffectiveness ratios were calculated using the discounted costs and QALYs.