Focusing on providers is key because healthcare expenses are so concentrated: High-cost cases account for the vast majority of the total. In those cases, the care provided is, as it should be, mainly the services and tests recommended by the provider. So if you do not influence provider recommendations in those cases, you cannot do all that much to improve the system. The evidence suggests, furthermore, that shifting away from paying for quantity and toward paying for quality affects what providers do in those high-cost cases. Although other quality- improvement measures can also influence provider behavior, the payment system is arguably the single most important determinant.