The goal of value-based purchasing is to reward clinicians and health care organizations that are able to achieve higher performance on quality measures. In principle, this is straightforward. But a challenge emerges when attempting to set a benchmark for payment. How high can quality get? For many measures, perfect (100% success or 0% failure) is theoretically possible. For example, it is possible that 100% of patients with coronary artery disease would either be prescribed antiplatelet therapy, have a valid contraindication, or make an informed choice to decline therapy.