In Chapter 4, we showed that there is significant variation in the number of parties under different electoral rules and political contexts, but we did not demonstrate the mechanisms – such as strategic defection by voters and elites – that underpin the different results we found. In Chapter 5, we began to show how rules and context shape strategic defection by voters under SMD rules, but the existence of a “personal” vote often obscured our view of much of the strategic voting that probably did occur. In this chapter, we introduce a different approach, which we use to highlight more directly how political context – most notably, democratic experience and party system development – conditions the impact of SMD rules on strategic defection in mixed-member electoral systems.
Specifically, we use Cox's (e.g., 1997) “SF ratio” measure (usually the vote total of the third-place contestant [the “Second loser”] divided by the vote total of the second-place contestant [the “First loser’]) to help draw inferences about strategic defection under particular electoral rules. As we do throughout this book, we use mixed-member systems to gain analytical leverage on electoral system effects. In this chapter we examine patterns of strategic defection in mixed-member systems in 41 elections in 11 different countries, considering how SF ratio patterns within a given country differ between the SMD and PR tiers of mixed-member systems. We show how SF ratio patterns in SMDs – unlike those in PR – often highlight the presence of strategic behavior, presumably because many voters and elites, when facing a competitive district race, transfer their support from candidates/parties who are unlikely to win to one of the top two contestants.