Early efforts to publish performance data about doctors and hospitals usually required a strong external force, such as pressure from a state department of health. But that’s changing. Some leading health care systems are now publishing ratings of their physicians on their own websites, not just ceding that activity to consumer outlets. This development may seem small, but if the trend grows, it will drive improvements in the quality of care. To envision that potential transformation, you first have to understand some of the origins of physician and hospital ratings.