Community-based aspects of therapeutic can influence the outcomes of pharmacoeconomic evaluations. OBJECTIVE: To evaluate the effect of incorporating data from RCTs versus data from community clinical practices on the results of an economic model of statins METHODS: The benefit of reducing LDL-C was incorporated into a model to calculate reduction in cardiovascular events and resulted economic outcomes. Data for LDL-C reduction from a head-to-head RCT [Am Heart J 2002;144:1044-51] were obtained for rosuvastatin (starting 5mg) versus atorvastatin (starting 10mg) with up-titration doses. A distribution of cardiovascular risk for users [N = 100,000, duration 5 years] in Canadian population [Clin Invest Med 2007;30:E63-E69] was assumed. Then, to illustrate the significance of the population level data, the data from the Canadian community-based clinical practice settings was removed from the model and the original RCT probability distribution for cardiovascular risk strata was applied into the model. RESULTS: Using community-based data modelling rosuvastatin and atorvastatin can prevent 9505 and 8702 cardiovascular events (non-fatal MI and stroke). Reduction in non-fatal MI and stroke can be translated to $252,300,392 (CDN), and $230,980,624 direct cost savings, respectively. Incorporating the RCT cardiovascular risk distribution, rosuvastatin and atorvastatin can prevent 7129 and 6712 cardiovascular events. This could lead to $180,214,565 and $178,152,982 direct cost savings for the Canadian healthcare system (adherence to therapy was assumed to be at the level of RCT). CONCLUSION: The distribution of cardiovascular risk was dissimilar between the RCT and the Canadian community-based data. The proportion of low risk patients enrolled in the RCT was significantly higher in comparison with the proportion of low risk patients on statin therapy in the Canadian community. Therefore, in this case the magnitude of cost savings would considerably be reduced if the RCT data were incorporated into the model instead of the community-based data.