The major problem is that the rankings were based on the perception of Deans, administrators, faculty and others  about the relative quality of the schools and not on any objective criteria that compared "apples to apples". The dental schools complained bitterly to US News and as a result US News has discontinued ranking US dental schools. Parenthetically, the dental schools were given wide acclaim by our colleagues in higher education as being the only education enterprise that has stood up to US News. As you may know, rankings of all colleges and universities are under intense criticism by our colleagues in the higher education community.