Electoral Studies 23 (2004) 575–599 www.elsevier.com/locate/electstud Mixed electoral systems and electoral system effects: controlled comparison and cross- national analysis Robert G. Moser a,Ã, EthanScheiner b,c a University of Texas at Austin, Austin, TX 78712, USA b Stanford University, Stanford, CA, USA c University of California at Davis, Davis, CA 95616, USA Abstract Utilizing data from 15 countries that employ mixed electoral systems, we provide a cross- national analysis of the defining elements and potentially constraining effects of such sys- tems. Using district level election results, we examine the effects of the proportional rep- resentation (PR) and single-member district (SMD) tiers of mixed systems separately and in combination. We also test the effects on electoral outcomes of different components of mixed systems such as linked tiers, ratio of SMD to PR seats, and majority versus plurality rules in the SMD tier. Our findings suggest that, despite claims of a ‘‘contamination effect’’ between the two tiers, in countries with developed party systems, PR and SMD electoral arrange- ments tend to approximate their expected effects even when used in combination in mixed systems. We also find that particular institutional characteristics within mixed systems have a substantial constraining effect on the number of significant political parties. However, the nature of the party system itself, in particular the extent to which its parties are institutiona- lized, also plays a very important role in shaping the degree to which constraining effects are truly felt. # 2003 Elsevier Ltd. All rights reserved. Keywords: Mixed electoral systems; Electoral system effects; Duverger’s law; Party institutionalization à Corresponding author. Tel.: +1-512-232-7278; fax: +1-512-471-1068. E-mail address: [email protected] (R.G. Moser). 0261-3794/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0261-3794(03)00056-8 576 R.G. Moser, E. Scheiner / Electoral Studies 23 (2004) 575–599 1. Introduction Mixed electoral systems, defined here as electoral systems that provide voters two votes for the legislature—one for a party list in a proportional representation (PR) tier and one for a candidate in a single-member district (SMD) tier—have emerged as a major alternative to strictly PR or SMD systems. This paper provides an analytical dissection of mixed electoral systems. Using district level data from 15 countries, we offer a comparative analysis of the effects of PR and SMD elec- toral arrangements when used simultaneously in mixed systems. Our approach offers several contributions to the growing literature on mixed electoral systems: first, we examine the effects of mixed systems in the widest var- iety of cases to date. Our dataset includes established democracies and new democ- racies from Europe, post-communist states, and Latin American countries, with systems that range from the long-standing institutionalized parties of Germany to the nearly inchoate party systems of Soviet successor states. Our study also pro- vides the most complete analysis we have found of the effects of different insti- tutional variations of mixed electoral systems, such as the impact of linked versus unlinked tiers. Finally, unlike many such cross-national studies of mixed systems, we use district level data to test relationships between electoral arrangements and party configurations, since theories of electoral system effects apply most directly to this level of analysis. With our data, we are able to analyze the independent influence of PR and SMD rules whencombinedinmixed electoral systems. The separate votes cast inthe PR and SMD portions of the balloting offer scholars an opportunity for ‘‘controlled comparison’’: mixed electoral systems represent a social laboratory in which effects of different types of electoral systems can be studied in isolation from influences of the social context such as social cleavages, socioeconomic development, or culture. Such an approach not only produces fresh insights on the effects of PR and SMD elections; but also explores the extent to which ‘‘contamination’’—the presence of PR balloting altering SMD politics and SMD balloting affecting PR—shapes the effects of electoral rules inmixed systems (see HerronandNishikawa, 2001; Cox and Schoppa, 2002). We find that PR and SMD electoral arrangements tend to approximate their expected effects evenwhenused incombinationif party systems are well developed. Our central findings focus on the factors that constrain the number of significant candidates and political parties. We find that particular institutional features within mixed systems—such as mechanisms linking the two tiers—constrain such numbers, but electoral institutional features are not alone in their constraining effects. We argue that the nature of the party system itself, in particular the extent to which a country’s party system is institutionalized, also plays a critical role in shaping the degree to which electoral system constraining effects are truly felt. Con- straining effects commonly attributed to electoral systems are much more likely at a certain level of party institutionalization. R.G. Moser, E. Scheiner / Electoral Studies 23 (2004) 575–599 577 2. Duverger’s law and its limits The electoral system literature is based onthree central Duvergerianpremises: PR systems tend to produce multi-party systems; two-ballot majoritarian systems promote multiple parties aligned into two camps; and plurality systems promote bipartism (Duverger, 1986, p. 70). Subsequent scholarship has better specified the nature of all these relationships. District magnitude (the number of representatives elected from each district) seems to be the decisive influence on multipartism and disproportionality in the translation of votes to seats. Low magnitudes, especially SMDs, have a powerful constraining effect on the number of parties and produce high disproportionality. High magnitudes allow (but do not cause) greater proliferation of parties and pro- duce less disproportionality (Taagepera and Shugart, 1989; Lijphart, 1994). The constraining effect of electoral systems seems to reside most directly at the district level rather than at the national level (Sartori, 1986, pp. 54–55; Cox, 1997). Cox (1997) explicates the limits of Duvergerianequilibria. District level strategic voting (and, by implication, strategic entry and departure by elites) requires certain conditions regarding actors’ motivations, preferences, time horizons, and avail- ability of accurate information. Plurality SMD elections may not reduce the vote for minor parties if any of the following holds: voters who are not short-term instrumentally rational; a lack of public information about voter preferences and vote intentions (and, hence, insufficient sense about which candidates are ‘‘out of the running’’); widespread certainty regarding likely winners; and the presence of many voters who strongly prefer their first choice and, thus, are nearly indifferent to other choices (Cox, 1997, p. 79). Even if conditions are favorable for establishing two-candidate races at the dis- trict level, bipartism projection to the national level is not assured. Projection depends on parties’ ability to unite prominent elites in single nationwide party organizations. If this is not accomplished, the two candidates produced in district level plurality elections may belong to many different parties across the country. Cox cites institutional factors, most notably the direct election of a powerful national executive, as the primary forces behind such nationalization (Cox, 1997, pp. 182–193). The pre-conditions for strategic behavior at the district level and projection of bipartism to the national level are particularly problematic during the initial elec- tions in new democracies, especially cases with little democratic tradition. The absence of previous electoral experience and accurate polling information may deny voters and elites the information necessary to behave strategically. The lack of well-established parties undermines the ability of voters and elites to behave strategically, as well as project to the national level constraining effects that occur at the district level. Where parties are new and weak, party ID among voters may be absent, so the main voting cues voters are left with involve the personal char- acteristics of candidates and patronage. In many new democracies, party organi- zations tend to be transitory, with parties continually entering and leaving the political arena (usually in step with the clout of their party leaders), thereby pro- 578 R.G. Moser, E. Scheiner / Electoral Studies 23 (2004) 575–599 viding little continuity between electoral periods. In such democracies, voters find it hard to cultivate lasting party preferences, leaving most uncommitted to any party. As we discuss below, party institutionalization has major consequences for elec- toral systems’ interaction with party systems. It would be a mistake to assume that institutionaleffects foundinestablished democracies will be replicated inthe very different context of new democracies in East Europe, Eurasia, and Latin America. Through our controlled comparison of PR and SMD tiers of mixed sys- tems in both consolidated and unconsolidated democracies, we can investigate the extent to which the level of party institutionalization conditions electoral system effects. Regarding specific effects of mixed electoral systems, Cox and Schoppa (2002) and HerronandNishikawa (2001) each argue cogently that there will be