Why do voters vote for third parties in single member districts? A test of four strategic voting conditions.

Duverger's law holds that single member district rules produce two-party systems, but third party voting remains an important feature of these institutional contexts. To explain the discrepancy between theory and empirical reality, Gary Cox specified four conditions that are necessary for the theoretical expectations to bear out. Yet, subsequent research has focused mostly on just one of these conditions, namely, that voters have correct information about the competitiveness of their preferred party in the district. The purpose of this paper is to assess the role of all four conditions. Using original survey data from the 2015 United Kingdom general election, the analysis suggests that violations of the information condition matter, but that violations of the short-term instrumental rationality condition can be a significant factor as well. Consequently, future research should pay more attention to this condition when seeking to explain third party voting. [ABSTRACT FROM AUTHOR]