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Robin E. Best and Steve B. Lem, "Electoral volatility, competition and third-party candidacies in US gubernatorial elections," Party Politics, 17 (September, 2011), 611-628. [Available at ]

First paragraph:
The participation of new or minor parties in elections can be puzzling, particularly when they stand little chance of winning the election. This puzzle is most likely to emerge under single-member-district plurality (SMD-p) electoral rules. The effect of electoral institutions on party system size is well established (Duverger, 1954; Ordeshook and Shvetsova, 1994; Rae, 1971; Riker, 1982) and SMD-p systems are known to place the most severe constraints on the number of viable candidates per electoral district (e.g. Cox, 1997). As Maurice Duverger astutely pointed out over 50 years ago, the use of SMD-p rules tends towards two-party systems (the Law), while the use of proportional representation (PR) often leads to multiparty systems (the Hypothesis). To explain the Law, Duverger argues that SMD-p rules discourage third parties due to (1) a mechanical effect, such that parties receiving less than a plurality of votes in a district receive no legislative seats, thereby increasing a candidate's incentives to run under a large party label, and (2) a psychological effect, where rational voters, recognizing their preferred (third-party) candidate will likely not win the election, cast their ballot for the ideologically closest (major-party) alternative.

Figures and Tables:
Table 1. The number of minor-party candidates, two-party vote difference and electoral volatility: summary statistics, 1980-2005a
Table 2. Negative binomial regression of the number of minor-party candidates
Figure 1. Difference in the two-party vote-share and in the number of third-party candidates
Figure 2. Electoral volatility and the number of third-party candidates

Last Paragraph:
We have demonstrated that two-party competition and electoral volatility affect the emergence of third-party candidacies in US gubernatorial elections. Furthermore, we believe the basic logic of our theory is applicable well beyond the context of US gubernatorial elections. By analysing the number of third-party candidates under the most restrictive electoral rules, we hope to have shed light on the factors that influence the emergence of new parties beyond prospects of winning the present election. As we have shown, small parties often emerge even when representational prospects are at their most bleak. Fluctuations in the numbers of parties contesting elections are commonly viewed as characteristics of newer democracies (e.g. Tavits, 2006), but we have shown that features of the electoral context, such as volatility, can also affect new entrants in established democracies. Perhaps more importantly, our theoretical focus on the electoral context illustrates how the incentives for new parties to emerge can vary from election to election. Thus, cross-national analyses of new party entries should also pay attention to election-specific characteristics. Small or minor parties are likely to have better prospects of influencing policy or gaining votes when the nature of electoral competition is in their favour.

Last updated August 2011