Scope Validity in Medicine

This chapter introduces scope validity as a conceptual tool to capture the (mis)matching of the scopes of disease operationalizations in different contexts of research and application. Drawing on examples of extrapolating results from animal models to human patient populations, the chapter proposes a shift in perspective away from idealized target constructs that can be hit and towards concrete practices of operationalization that render diseases researchable. It argues that we need to take seriously the locally varying conditions under which disease concepts operate and that impact on the assessment of a model’s validity. Combining an adequacy-for-purpose view towards validity with a practice-oriented, pragmatist and particularistic perspective on disease concepts, the chapter presents scope validity as a relational concept that does not presuppose the extent of a test or model’s generalizability to some hypothetical ideal. This offers us a possibility to distinguish between a model’s high external validity for a small patient population, and a model’s broad scope of applicability. Scope validity thus does not replace other validity concepts, such as predictive validity, external validity and construct validity, but rather helps to clarify and qualify the frame and conditions under which a model or test’s validity should be assessed, putting the question of adequacy in medical research to the forefront.