There is no such ranking system. It is based on reputation and word-of-mouth. US News and some of the parenting magazines rank the best children's hospitals each year. They do use some objective criteria such as surgical outcomes and nursing support, but the majority of the ranking comes from "reputation".
So it is kind of abstract, yet most people would agree on which programs are generally the most well-respected. The problem becomes who belongs on the 2nd, 3rd, 4th and so on Teirs-this is highly debatable.
