Interest in the EBM philosophy of evidence has led philosophers to consider the nature of EBM’s hierarchy of evidence, which rank different kinds of research methodology, ostensibly, by the relative evidential weight they provide. While Jeremy Howick provides a critical defense of EBM,[8] most philosophers have raised questions about its legitimacy. Key questions asked about hierarchies of evidence concern the legitimacy of ranking methodologies in terms of the strength of support that they supply;[12][13] how instances of particular methods may move up and down a hierarchy;[14] as well as how different types of evidence, from different levels in the hierarchies, should be combined.