There are various ways in which data for economic evaluations may be obtained, including via clinical trials and via economic modelling. There are numerous advantages and disadvantages associated with each method, although it is generally assumed that economic models lack the accuracy required for the calculation of meaningful cost-effectiveness data. In order to assess the predictive accuracy of economic modelling in the context of cholesterol-modifying pharmacotherapy it is possible to compare predicted coronary heart disease (CHD) incidence estimates obtained using CHD risk equations derived from the Framingham Heart Study (FHS) with actual CHD incidence rates achieved in a major clinical trial, the West of Scotland Coronary Prevention Study (WOSCOPS). FHS-derived CHD risk equations substantially underestimate the actual risks of nonfatal myocardial infarction obtained by WOSCOPS. However, in predicting risks of death from CHD, FHS-derived CHD risk equations estimate extremely accurately the incidence obtained by WOSCOPS. For example, from WOSCOPS the risk of an individual fulfilling the trial entry criteria incurring nonfatal myocardial infarction or CHD death in 4.9 years is 0.079 for placebo group and 0.055 for the intervention group. Therefore, the relative risk for the intervention group relative to placebo group is 0.696, implying a risk reduction of 30%. Comparable risks predicted using FHS-derived CHD risk equations are 0.116 for the placebo group and 0.088 for the intervention group. Consequent relative risks and risk reductions for the intervention relative to placebo are 0.757 and 24%, respectively. Using both model and trial estimates of CHD incidence in an economic evaluation of cholesterol-modifying pharmacotherapy, incremental costs per life year gained are ยฃ41 707 using WOSCOPS data and ยฃ36 480 using FHS-derived CHD risk equations.