Surgeon-level reporting may also increase the potential for risk aversion, as the anticipated worse results of the highest-risk patients are not diluted by the larger volume of a hospital or group. Finally, because the distribution of patient severity may vary substantially among providers, direct comparison of the results of one surgeon or hospital with those of another, even by using indirectly risk- standardized results, is often inappropriate.788 Rather, these results should be interpreted as comparisons of a provider s outcomes for his or her specific patient cohort versus what would have been expected had those patients been cared for by an average provider in the benchmark population. Although risk-adjusted mortality rate has been the domi- nant performance metric in cardiac surgery for 2 decades, other more comprehensive approaches have been advo- cated.789 The STS CABG composite illustrates one such multidimensional approach, consisting of 11 National Quality Forum endorsed measures of cardiothoracic surgery perfor- mance grouped within 4 domains of care.619,790 5.1.1. Use of Outcomes or Volume as CABG Quality Measures: Recommendations Class I 1. All cardiac surgery programs should participate in a state, regional, or national clinical data registry and should receive periodic reports of their risk-adjusted outcomes. (Level of Evidence: C) Class IIa 1. When credible risk-adjusted outcomes data are not available, volume can be useful as a structural metric of CABG quality.309,751,791 798,800 804,807,818 (Level of Evidence: B) Class IIb 1. Affiliation with a high-volume tertiary center might be considered by cardiac surgery programs that perform fewer than 125 CABG procedures annually. (Level of Evidence: C) See Online Data Supplement 32 for additional data on outcomes or volume as CABG quality measures. 