Measurements: The percentage of graduates who practice primary care, work in health professional shortage areas, and are underrepresented minorities, combined into a composite social mission score.
Here's a partial list of the ranking---top and bottom 20. Here's the complete listing for each of the measurement categories and for the composite score. What's interesting is that medical schools traditionally considered among the nation's best tended to be rated near the bottom. There's an interesting irony in my med school home town, Nashville. Vanderbilt, my alma mater, ranked last---dead last---among the 140 schools. Meharry Medical College across town ranked second. This was despite the fact that the two schools formed an alliance over ten years ago, to try and close the gap.
In fairness, Vandy is a research-heavy medical school with a strong dedication to the training and nurturing of physician-scientists. While the school has produced hundreds of primary care docs, a large percentage of students gravitate to subspecialties, basic research and academic medicine. We need physician-scientists as teachers and researchers just as we need PCPs.