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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.

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.

Nearly all systematic empirical work on the relationship between social diversity and the number of parties asserts the "interactive hypothesis"—Social heterogeneity leads to party fragmentation under permissive electoral rules, but not under single-member district, first-past-the-post (FPTP) rules. In this article, we argue that previous work has been hindered by a reliance on national-level measures of variables and a linear model of the relationship between diversity and party fragmentation. This article provides the first analysis to test the interactive hypothesis appropriately by using district-level measures of both ethnic diversity and the effective number of parties in legislative FPTP elections and considering a curvilinear relationship between the variables. We find that there is a strong relationship between social diversity and the number of parties even under FPTP electoral rules, thus suggesting that restrictive rules are not as powerful a constraint on electoral behavior and outcomes as is usually supposed.

Political science knows a fair amount about the variables explaining party systems fragmentation or the constant in the equation of the number of parties. But we know much less about changes in the number of parties over time within countries or the slope in the equation of the number of parties. This paper fills this gap explaining the entry of new viable competitors in party systems after the founding election. Using empirical evidence from Spain, we show that when there is an electoral market failure and the higher the number of perfectly elastic voters, the higher the probability of new viable entrants. ; La ciencia política tiene un conocimiento bastante extenso de las variables que explican el sistema de fragmentación de partidos o de la constante en la ecuación del número de partidos. Pero, en cambio, se sabe mucho menos sobre los cambios en el número de partidos en el tiempo en los países o la pendiente de la ecuación en el número de los partidos. Este trabajo viene a cubrir esta carencia al explicar la entrada de los nuevos competidores viables en el sistema de partidos después de la elección fundacional. Utilizando la evidencia empírica de España, mostramos que cuando hay un fallo del mercado electoral y cuanto mayor es el número de votantes perfectamente elásticos, mayor es la probabilidad de nuevas entradas viables.

Political science knows a fair amount about the variables explaining party systems fragmentation or the constant in the equation of the number of parties. But we know much less about changes in the number of parties over time within countries or the slope in the equation of the number of parties. This paper fills this gap explaining the entry of new viable competitors in party systems after the founding election. Using empirical evidence from Spain, we show that when there is an electoral market failure and the higher the number of perfectly elastic voters, the higher the probability of new viable entrants. ; La ciencia política tiene un conocimiento bastante extenso de las variables que explican el sistema de fragmentación de partidos o de la constante en la ecuación del número de partidos. Pero, en cambio, se sabe mucho menos sobre los cambios en el número de partidos en el tiempo en los países o la pendiente de la ecuación en el número de los partidos. Este trabajo viene a cubrir esta carencia al explicar la entrada de los nuevos competidores viables en el sistema de partidos después de la elección fundacional. Utilizando la evidencia empírica de España, mostramos que cuando hay un fallo del mercado electoral y cuanto mayor es el número de votantes perfectamente elásticos, mayor es la probabilidad de nuevas entradas viables.

El presente artículo examina el caso de las reformas al sistema electoral municipal venezolano en el período comprendido entre 1984 y 1995 con la finalidad de comprobar teorías sobre las implicaciones del sistema electoral en el sistema de partidos. Examinamos el efecto de la magnitud de la circunscripción electoral, el umbral de representación y la fórmula electoral en el número efectivo de partidos electorales y legislativos. Se argumenta que las sucesivas reformas generaron expectativas que incentivaron a una mayor participación de los partidos políticos y grupos de electores en las contiendas electorales locales pero que no resultaron en un número significativo de nuevos escaños para éstos, lo que contribuyó a la desconfianza en la institución electoral y a la larga, a deslegitimar aún más a los dos partidos tradicionales. ; This article examines electoral reforms to the Venezuelan municipal electoral system between 1984 y 1995 to confirm theories on the effect of the electoral system on the party system. We examine the effect of district magnitude, electoral threshold and the electoral formula on the effective number of electoral and legislative parties. We affirm that successive reforms generated expectations that encouraged many political parties and electoral groups to compete in local elections, but that those reforms did not result in a significant number of additional seats for them. This contributed to the furtber erosion of public trust in the electoral institution and in the two traditional political 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.

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.

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.