In This Article Expand or collapse the "in this article" section Mixed-Member Electoral Systems

  • Introduction
  • Classification and Theoretical Development: Books
  • Classification and Theoretical Development: Articles
  • Voting Behavior
  • Consequences for Elections and Party Systems
  • Representation and Policy Outcomes
  • Legislative Behavior and the Mandate Divide
  • Regional Studies: Germany and Japan
  • Regional Studies: New Zealand
  • Regional Studies: Central and Eastern Europe
  • Regional Studies: Other Countries

Political Science Mixed-Member Electoral Systems
Erik S. Herron
  • LAST MODIFIED: 26 November 2019
  • DOI: 10.1093/obo/9780199756223-0292


Scholarship on the classification, origins, incentives, and consequences of mixed-member electoral systems has matured, especially over the last two decades. While mixed-member electoral systems (also known as mixed electoral systems) have been in constant use since Germany adopted a mixed-member proportional system for assembly elections following World War II, researchers did not begin to fully probe the implications of this electoral system until its expansion across the globe beginning in the 1990s. Mixed-member electoral systems share an important characteristic: voter preferences are translated into outcomes by at least two allocation formulas applied in the same election. While voters typically receive a ballot to select a representative in a constituency (often using first-past-the-post) and a ballot to select a party list (often using a form of proportional representation (PR)), the institutional features of mixed-member systems vary substantially. A crucial distinction among mixed-member systems is whether or not seat allocation in the constituency and proportional representation tiers is linked (mixed-member proportional, or MMP) or unlinked (mixed-member majoritarian, or MMM). Across the universe of mixed-member systems, one finds additional differences in the number of ballots voters receive; the electoral formulas and thresholds used to determine winners; the proportion of seats allocated to each component; the ability of candidates to contest seats in both components during the same election; and other critical aspects of the rules. Scholarship classifying mixed-member systems has highlighted different aspects of the rules to sort them into categories. A substantial amount of scholarship on mixed-member systems has emphasized the debate about the incentives that the systems generate. The “controlled comparison” approach treats the components as if they are independent from one another and the “contamination effects” approach treats the components as if they are interdependent. These competing schools of thought generate different expectations, with the former generally anticipating compliance with Duverger’s propositions and the latter anticipating divergence. Subsequent scholarship has been split about which approach better explains observed behavior. However, many of the perceived differences between the approaches may be artificial, generated by extreme interpretations of the theoretical expectations that lack appropriate nuance. In other words, it may be inappropriate to treat this scholarship as strictly dichotomous. The extant literature on mixed-member systems evaluates data from surveys, interviews, personnel files, roll-call voting, and election returns to understand the behavior of voters, candidates, parties, and legislators. It assesses how the incentives of mixed-member systems contribute to outcomes such as the party system, descriptive representation, and policy decisions. It also explores the presence or absence of a “mandate divide”: the expectation that members of parliament (MPs) selected in the constituency component might behave differently than their counterparts in the party list component. The research is often cross-national, but studies of certain countries with mixed-member systems predominate: Germany, Japan, and New Zealand among established democracies, and central or east European countries among transitional societies. The literature presents many opportunities to generate more nuanced theory, explore different research methodologies (e.g., experimental work), and extend spatial coverage to under-studied countries.

Classification and Theoretical Development: Books

Shugart and Wattenberg 2001 provides an overview of mixed-member systems. Moser 2001 and Moser and Scheiner 2012 summarize the controlled comparison approach while Ferrara, et al. 2005 presents the contamination effects approach.

  • Ferrara, Federico, Erik S. Herron, and Misa Nishikawa. Mixed Electoral Systems: Contamination and Its Consequences. New York: Palgrave Macmillan, 2005.

    Defines and empirically demonstrates contamination effects in mixed-member systems. The book features chapters about the effects of contamination on voter, party, and legislative behavior.

  • Moser, Robert G. Unexpected Outcomes: Electoral Systems, Political Parties, and Representation in Russia. Pittsburgh, PA: Pittsburgh University Press, 2001.

    The first study to fully articulate the “controlled comparison” approach, applying it to the study of Russian politics.

  • Moser, Robert G., and Ethan Scheiner. Electoral Systems and Political Context: How the Effects of Rules Vary Across New and Established Democracies. Cambridge, UK: Cambridge University Press, 2012.

    Extends the controlled comparison approach, emphasizing how the context in which elections are conducted affects party systems, women’s representation, and other outcomes.

  • Shugart, Matthew S., and Martin P. Wattenberg, eds. Mixed-Member Electoral Systems: The Best of Both Worlds? Oxford: Oxford University Press, 2001.

    The first comprehensive book-length treatment of mixed-member systems, covering classification, origins, and consequences.

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