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This paper proposes a model of a legislature, formed by several parties, which has to vote for or against a certain bill in the presence of a lobbyist interested in a certain vote outcome. We show that the ease with which the lobbyist can manipulate a legislature decision increases with the number of elected parties, and, consequently, decreases with an electoral threshold. On the other hand, a lower electoral threshold increases the representativeness of a legislature. We combine these two effects in a notion of fairness. We show the existence of an electoral threshold that optimizes the fairness of a political system, which is close to 1–5%. Namely, the optimal threshold (in our sense) is close to thresholds that exist in most parliamentary democracies.

This paper proposes a model of a legislature, formed by several parties, which has to vote for or against a certain bill in the presence of a lobbyist interested in a certain vote outcome. We show that the ease with which the lobbyist can manipulate a legislature decision increases with the number of elected parties, and, consequently, decreases with an electoral threshold. On the other hand, a lower electoral threshold increases the representativeness of a legislature. We combine these two effects in a notion of fairness. We show the existence of an electoral threshold that optimizes the fairness of a political system, which is close to 1-5%. Namely, the optimal threshold (in our sense) is close to thresholds that exist in most parliamentary democracies.

Altres ajuts: COST Action IC1205 on Computational Social Choice ; This paper proposes a model of a legislature, formed by several parties, which has to vote for or against a certain bill in the presence of a lobbyist interested in a certain vote outcome. We show that the ease with which the lobbyist can manipulate a legislature decision increases with the number of elected parties, and, consequently, decreases with an electoral threshold. On the other hand, a lower electoral threshold increases the representativeness of a legislature. We combine these two effects in a notion of fairness. We show the existence of an electoral threshold that optimizes the fairness of a political system, which is close to 1-5%. Namely, the optimal threshold (in our sense) is close to thresholds that exist in most parliamentary democracies.

Polarization is a key characteristic of party systems, but scholars disagree about how polarization relates to the number of parties in a system. Different authors find positive, negative, or null relationships. This relationship is what one would expect if parties were drawn randomly from a super-population with an effective sample size somewhere between the effective and raw number of parties. I test this claim using multiple datasets which report party positions and seat shares, before extending my analysis to consider vote-level polarization, the range of positions, and polarization in presidential and parliamentary regimes. My work extends the Taageperaan research agenda of building interlocking networks of equations relating key quantities of electoral and party systems.

This note helps to explain how cabinet-level concentration of power is constrained by party level concentration of seats. Arend Lijphart's Patterns of Democracy (1999) measures concentration of executive power by the frequency of minimal winning and one-party cabinets (MW/OP), and party concentration by the effective number (N) of legislative parties. In his factor analysis, these highly correlated indices are the central features that distinguish consensual from majoritarian systems. The present study establishes a quantitative logical relationship leading from N to the major component of MW/OP, so as to explain the reasons behind Lijphart's empirical observation. The note analyses separately the frequency of various types of cabinet coalitions that Lijphart's book has lumped together. It also offers a new way to visualize the effective number of legislative parties, as twice the minimal number of parties needed to form a minimal winning coalition. © 2002, Sage Publications. All rights reserved.

Scholars studying electoral systems have consistently found that single-member plurality elections tend to constrain the number of parties operating in a polity to a much greater extent than multimember proportional representation systems. This article tests this hypothesis in the post-communist context by examining the effects of proportional representation and single-member district elections on the number of parties in five postcommunist states. It is shown that some postcommunist states, most notably Poland and Hungary, have followed the standard pattern of party consolidation over time in reaction to incentives of electoral systems, while others, most notably Russia and Ukraine, have not. The author argues that the different effects of electoral systems can be attributed to different levels of party institutionalization found in postcommunist states.These findings have policy implications. Under conditions of extreme party underdevelopment, the electoral system that promotes the use of party labels—proportional representation—may be more effective than the plurality system in constraining the number of parties, provided a legal threshold is used. This runs counter to the conventional wisdom that plurality elections offer the greatest constraint on the number of parties.

In an exploration of the ways that electoral institutions influence party systems, & the extent to which electoral laws mediate the influence of ethnic heterogeneity, data from earlier studies by Douglas Rae (1967) & Arend Lijphart (1990) are reanalyzed to reconsider the role of one institutional parameter -- district magnitude. It is concluded that district magnitude is not merely an important determinant of the number of parties that compete in a political system, but can offset the tendency of parties to multiply in ethnically heterogeneous societies. 5 Tables, 25 References. Adapted from the source document.

To date, electoral systems are conceptualised as setting an 'upper bound' to, or defining a 'carrying capacity' for, the number of parties or lists, and their effect is assessed at the district level. This article adds to the empirical study of electoral systems by analysing a vast database of district-level electoral returns. The argument focuses on the demand and supply of viable electoral candidates, which are conditioned by the interplay of strategic entry (by the party rank and file) and strategic voting (by the electorate). Drawing on a database of almost 18,000 electoral districts taken from 15 West European countries, the empirical analysis yields a number of insights: most specifically, (1) district magnitude only becomes binding and effective when a higher social demand meets a lower carrying capacity of the electoral district; (2) the provision of upper tiers undermines the emergence of Duvergerian equilibria within the primary electoral districts. Adapted from the source document.

Duverger's propositions concerning the psychological and mechanical consequences of electoral rules have previously been examined mainly through the lens of district magnitude, comparing the properties of single-member district plurality elections with those of multimember proportional representation elections. The empirical consequences of multimember plurality (MMP) rules, on the other hand, have received scant attention. Theory suggests that the effect of district magnitude on the number and concentration of parties will differ with regard to whether the allocation rules are plurality-based or proportional. I test this theory by drawing on a uniquely large-sample dataset where district magnitude and electoral formula vary but the basic universe of political parties is held constant, applying regression analysis to data from several thousand Hungarian local bodies elected in 1994 consisting of municipal councils, county councils, and mayors. The results indicate that omitting the variable of electoral formula has the potential to cause significant bias in estimates of Duvergerian consequences of district magnitude. In addition, the analysis of multimember plurality elections from the local election dataset reveals counter-intuitively that candidate and party entry may increase with district magnitude under MMP, suggesting important directions for future investigation of MMP rules. (European Journal of Political Research / FUB)