Boundaries of Disease: Vagueness and Overdiagnosis.

In five related essays, Mary Jean Walker and Wendy Rogers, joined in one essay by Jenny Doust, defend various theses about the concept of disease. First, they argue "disease" is a cluster concept, not a "classically structured" one definable by necessary and sufficient conditions. Second, "disease" is vague, in the standard philosophical sense of having borderline cases. In fascinating detail, they argue that this vagueness shows up almost everywhere one looks among ordinary diseases, even if disease is taken to require dysfunction. Still, they conclude, vagueness per se need not be a problem because logicians and philosophers know several ways to handle it. Third, Rogers and Walker believe that the vagueness of "disease" is a clue to how to reduce the much-discussed medical problem of "overdiagnosis": the diagnosis of permanently harmless disease. Finally, they find my analysis of disease-the "biostatistical theory" (BST)-defective and dangerous in four different ways: it offers insufficient guidance on how to draw disease boundaries; it does not fit actual medical practice in doing so; it is ambiguous as to reference class; and it facilitates overdiagnosis. In this article, I freely concede the vagueness of disease, but argue that it is considerably less than Rogers and Walker suppose, and no threat to the BST in any case. I also rebut all their other charges of deficiency in my analysis.