Extension of the portfolio allocation model to surplus majority governments: a fuzzy approach

Scholars have long studied the conditions under which the cabinet making process will result in minority, surplus majority, or minimum-winning governing coalitions in parliamentary systems. Since Riker, a good number of these attempts have been based on rational choice assumptions. Among formal approaches in this vein, Laver and Shepsle’s (Making and breaking governments: Cabinets and legislatures in parliamentary governments, 1996) portfolio allocation model argues that parties centrally located in policy space have a greater potential for being part of any governing coalition and that parties located at the issue-by-issue median have a high likelihood of forming a minority government. However, the model predicts that surplus majority coalitions will only form when the number of salient policy dimensions in the political system is greater than two. We incorporate fuzzy set theory in the portfolio allocation model, permitting us to model ambiguity in parties’ policy preferences. The reformulated model accounts for the formation of surplus majority coalitions in two-dimensional policy space. We illustrate the model’s conclusions with a case study of the 1996 surplus majority coalition in the Lithuanian Seimas.