The impact of using different costing methods on the results of an economic evaluation of cardiac care: microcosting vs gross-costing approaches

Background: Published guidelines on the conduct of economic evaluations provide little guidance regarding the use and potential bias of the different costing methods. <P>Objectives: Using microcosting and two gross-costing methods, we (1) compared the cost estimates within and across subjects, and (2) determined the impact on the results of an economic evaluation. Methods: Microcosting estimates were obtained from the local health region and gross-costing estimates were obtained from two government bodies (one provincial and one national). Total inpatient costs were described for each method. Using an economic evaluation of sirolimus-eluting stents, we compared the incremental cost-utility ratios that resulted from applying each method. Results: Microcosting, Case-Mix-Grouper (CMG) gross-costing, and Refined-Diagnosis-Related grouper (rDRG) gross-costing resulted in 4-year mean cost estimates of $16 684, $16 232, and $10 474, respectively. Using Monte Carlo simulation, the cost per QALY gained was $41 764 (95% CI: $41 182-$42 346), $42 538 (95% CI: $42 167-$42 907), and $36 566 (95% CI: $36 172-$36 960) for microcosting, rDRG-derived and CMG-derived estimates, respectively (P<0.001). Conclusions: Within subject, the three costing methods produced markedly different cost estimates. The difference in cost-utility values produced by each method is modest but of a magnitude that could influence a decision to fund a new intervention. Copyright © 2008 John Wiley & Sons, Ltd.