Disease, variety, disagreement, and typicality: Advantage Roschian Concepts?

In a classical approach, disease is defined in terms of necessary and sufficient conditions. In contrast, in a Roschian approach, the degree of similarity to a prototype determines membership in the class of diseases. Because Roschian approaches recognize degrees of similarity among members of the category, and do not assert that all diseases must be the essentially the same, it can be argued that they have certain advantages, at a general level. These include accommodation of the variety of diseases, the capacity to explain disagreement about category membership, and to account for typicality effects (where people see some diseases as typical and some as less typical of the category). But despite the expectation, Roschian accounts do not unproblematically accommodate disease variety, do not make a better job of explaining disagreement about disease status, and turn out to be as embarrassed by typicality effects as classical approaches.