The Seat Product Model of the effective number of parties: A case for applied political science

2016 ◽  
Vol 41 ◽  
pp. 23-34 ◽  
Author(s):  
Yuhui Li ◽  
Matthew S. Shugart
Keyword(s):  
Political Science ◽  
Effective Number ◽  
Product Model ◽  
Effective Number Of Parties ◽  
Number Of Parties

scholarly journals Predicting the Number of Parties: A Quantitative Model of Duverger's Mechanical Effect

1993 ◽  
Vol 87 (2) ◽  
pp. 455-464 ◽  
Author(s):  
Rein Taagepera ◽  
Matthew Soberg Shugart
Keyword(s):  
National Level ◽  
Quantitative Model ◽  
Mechanical Effect ◽  
Structural Constraints ◽  
Effective Number ◽  
Institutional Variables ◽  
National Assembly ◽  
Effective Number Of Parties ◽  
Number Of Parties ◽  
Great Portion

The mechanical effect of electoral systems, identified by Maurice Duverger, can be estimated by means of a quantitative model. The model predicts the range within which the effective number of parties in a district should fall for a given magnitude (number of seats) of the district. At the national level, a related model predicts the effective number of parties based on the effective magnitude and the number of seats in the national assembly. The institutional variables considered—magnitude and assembly size—define a great portion of the structural constraints within which a given country's politics must take place. The model developed provides a good fit to data in spite of its having been developed from outrageously simple starting assumptions.

Crowded Space, Fertile Ground: Party Entry and the Effective Number of Parties

2015 ◽  
Vol 4 (2) ◽  
pp. 317-342 ◽  
Author(s):  
Daniel M. Kselman ◽  
Eleanor Neff Powell ◽  
Joshua A. Tucker
Keyword(s):  
Political Parties ◽  
Party System ◽  
Status Quo ◽  
Policy Implications ◽  
Policy Outcomes ◽  
Effective Number ◽  
Data Set ◽  
Fertile Ground ◽  
Effective Number Of Parties ◽  
Number Of Parties

This paper develops a novel argument as to the conditions under which new political parties will form in democratic states. Our approach hinges on the manner in which politicians evaluate the policy implications of new party entry alongside considerations of incumbency for its own sake. We demonstrate that if candidates care sufficiently about policy outcomes, then the likelihood of party entry shouldincreasewith the effective number of status quo parties in the party system. This relationship weakens, and eventually disappears, as politicians’ emphasis on “office-seeking” motivations increases relative to their interest in public policy. We test these predictions with both aggregate electoral data in contemporary Europe and a data set on legislative volatility in Turkey, uncovering support for the argument that party system fragmentation should positively affect the likelihood of entry when policy-seeking motivations are relevant, but not otherwise.

The Number of Parties and Party System Nationalization in an Integrated Analytical Framework

2015 ◽  
Vol 14 (5) ◽  
pp. 662-681
Author(s):  
Grigorii V. Golosov
Keyword(s):  
Party System ◽  
Empirical Test ◽  
Analytical Framework ◽  
Direct And Indirect Effects ◽  
Effective Number ◽  
Regional Parties ◽  
Methodological Tool ◽  
Effective Number Of Parties ◽  
Nuanced Understanding ◽  
Number Of Parties

This study develops a methodological tool for integration of research on party system fragmentation and party system nationalization. The method is built by decomposing a standard indicator of fragmentation, the effective number of parties, into individual-party components (effective size scores), and weighting them by nationalization scores, which allows for disaggregating the number of parties into two distinct components, the effective numbers of national and regional parties. As a result, it becomes possible to assess the influences of substantively important factors upon the components of the number of parties and the overall level of fragmentation in a methodologically consistent, quantifiable way. In addition, the proposed framework of analysis differentiates between direct and indirect effects upon party system fragmentation. A preliminary empirical test on a sample from 90 countries demonstrates that the proposed framework for analysis allows for achieving a rich and nuanced understanding of the factors of party system fragmentation.

Predicting Party Systems from Electoral Systems

2020 ◽  
Author(s):  
Rein Taagepera ◽  
Matthew Shugart
Keyword(s):  
Political Science ◽  
Party System ◽  
Electoral Systems ◽  
Party Systems ◽  
Product Model ◽  
District Magnitude ◽  
Upper Limits ◽  
Predictive Relationships ◽  
Number Of Parties ◽  
Quantities Of Interest

The Seat Product Model matters to electoral and party systems specialists in what it is able to predict, and to all political scientists as one example of how to predict. The seat product (MS) is the product of assembly size (S) and electoral district magnitude (M, number of seats allocated). Without any data input, thinking about conceptual lower and upper limits leads to a sequence of logically grounded models that apply to simple electoral systems. The resulting formulas allow for precise predictions about likely party system outputs, such as the number of parties, the size of the largest party, and other quantities of interest. The predictions are based entirely on institutional inputs. And when tested on real-world electoral data, these predictions are found to explain over 60% of the variance. This means that they provide a baseline expectation, against which actual countries and specific elections can be compared. To the broader political science audience, this research sends the following message: Interconnected quantitatively predictive relationships are a hallmark of developed science, but they are still rare in social sciences. These relationships can exist with regard to political phenomena if one is on the lookout for them. Logically founded predictions are stronger than merely empirical relationships or predictions of the direction of effects. Finally, isolated equations that connect various factors are nice, but equations that interconnect pack even more predictive punch. Political scientists should strive for connections among connections. This would lead to a more scientific political science.

The Effect of District Magnitude on Electoral Outcomes: Evidence from Two Natural Experiments in Argentina

2017 ◽  
Vol 49 (2) ◽  
pp. 557-577 ◽  
Author(s):  
Adrián Lucardi
Keyword(s):  
Psychological Effect ◽  
Effective Number ◽  
Natural Experiments ◽  
Electoral Rules ◽  
Electoral Outcomes ◽  
District Magnitude ◽  
Electoral Support ◽  
Effective Number Of Parties ◽  
Number Of Parties

How does district magnitude affect electoral outcomes? This article addresses this question by exploiting a combination of two natural experiments in Argentina between 1985 and 2015. Argentine provinces elect half of their congressional delegation every two years, and thus districts with an odd number of representatives have varying magnitudes in different election years. Furthermore, whether a province elects more representatives in midterm or concurrent years was decided by lottery in 1983. I find that district magnitude (a) increases electoral support for small parties, (b) increases the (effective) number of parties that gain seats and (c) reduces electoral disproportionality. The last two results are driven by the mechanical rather than the psychological effect of electoral rules.

The Effective Number of Parties

2009 ◽  
Vol 16 (2) ◽  
pp. 171-192 ◽  
Author(s):  
Grigorii V. Golosov
Keyword(s):  
Effective Number ◽  
Effective Number Of Parties ◽  
Number Of Parties
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