Li J, et al. - Physician Compare is the CMS’ flagship website about the quality of care provided by doctors and other clinicians in the United States. The website is in its final expansion phase, focusing on the addition of clinician-level performance data to existing practice-level data in order to further assist patients and caregivers with selecting high-quality clinicians. But it is unclear whether Physician Compare is comprehensive: reporting is voluntary; clinicians choose the measures; and CMS displays a subset of measures. Thus, using current data from Physician Compare, investigators aimed to address three questions: How many and what types of clinicians have quality information? How comprehensive are the quality data? How well do the measures differentiate the performance of included clinicians?