Limited diversity and QCA solution types: assumptions and their consequences

Limited diversity is a term employed in the context of Ragin’s Qualitative Comparative Analysis (QCA), but it describes a phenomenon which is widespread in social contexts: cases are usually not distributed evenly across all the possible combinations of factors linked to some outcome. Instead, they are often clustered together. To deal with limited diversity, the three solution types parsimonious, intermediate, and complex (or conservative) solution have been proposed. There is an ongoing debate as to the merits of each solution type. This paper contributes to the debate by focussing on what the implications of choosing each solution type are. In making this choice, researchers have to make certain assumptions, and the paper discusses what these are and how they vary depending on which solution type is being implemented, drawing on invented examples and examples from published work to bring out the consequences of these assumptions. It concludes that it is not obvious that any one solution type is superior, certainly not to the degree that the others always have to be ruled out. They rely on different kinds of assumptions and models of causation. Thus, depending on the research situation, it may be helpful to analyse different scenarios, including one(s) where we assume that our initial assumptions are wrong. Ideally, researchers are able to take steps to reduce or eliminate limited diversity since none of the existing solution types are without problems. However, since this is not always possible, it is best to be aware of the consequences of choices.