The Book

The chapter describes relationships among parties—interparty politics—and relationships within parties—intraparty politics. Understanding the reasons for variations in these party politics across countries (and over time) is fundamental to understanding why citizens get the forms of representation they get. The variations in interparty and intraparty politics that we see around the world are at least in part—perhaps in large part—due to the electoral systems countries use to elect their public official. After developing a conceptual framework for depicting the richness of party politics, the chapter includes a description of the structure of the rest of the book and the other materials the project provides.

Electoral systems are sets of formal rules that create incentives for strategic behavior on the part of voters, (pre-) candidates, party elites, and elected representatives, including rank-and-file legislators and their party bloc leaders. The translation of votes into seats won by candidates and parties is governed by specific rules. As a result, these rules shape the behavior of candidates during campaigns, affect voters’ decision-making processes, and guide representatives’ actions in office. As indicated in Chapter 1, the combination of electoral rules to form an electoral system sets the incentives for both interparty and intraparty political conduct. This chapter defines the electoral rules that define every electoral system. The rules thought to influence interparty politics are district magnitude, the seat allocation formula, and legal thresholds. The rules thought to influence intraparty politics are ballot access, ballot type, vote pooling, number and level of votes cast, and district magnitude.

The chapter divides electoral systems into three groups or families: majoritarian, proportional and mixed. Proportional systems allot multiple seats in each district, and to a greater or lesser degree their rules tend to assure that political parties obtain legislative seats in proportion to their vote share. Pluralitarian/majoritarian systems, by contrast, often award just one seat, and the largest party receives that only seat. If multimember districts are then used, the largest parties often receive significantly more seats than the proportion of votes they earned. Mixed-member systems combine elements of the other two families by establishing one tier that awards seats according to proportional representation and a second tier that distributes seats based on majority/plurality. The chapter discusses the commonalities across systems that are shared by members of a given family, and then uses the electoral rules covered in the previous chapter to define individual systems, pointing out characteristics they share or do not share with other systems in the same family. Summary tables give readers succinct reference points they can use as they read the remainder of the book.

The chapter makes the case for why computer simulations are needed to understand electoral system incentives, contrasting this approach with others. It presents the details of the simulation exercise, explaining the choices the authors made at every step of the simulation algorithm. The chapter concludes with a reminder of the kinds of measurements the simulated election results can provide, emphasizing the ability to “map” electoral systems on an Interparty–Intraparty spatial continuum. It concludes with a discussion of the potential to use these simulations to answer other related questions.

This chapter evaluates how each of the component rules of electoral systems relates to the book’s two main quantities of interest. Chapter 2 and Chapter 3 speculated that Total Duvergerian Effect (TDE)—the indicator of interparty incentives—would primarily be a function of district magnitude, seat allocation formula, and electoral threshold and that Average Personalism (AP)—the indicator of intraparty incentives—would primarily be a function of ballot type, number and level of votes, vote pooling, district magnitude, and ballot type. Chapter 4 presented a simulation framework that helped us observe—in a controlled setting, without the confounding factors that typically plague observational data—the potential inter- and intraparty incentives generated by different types of electoral systems. Now we can tease out the influence of individual rules that go into the making of each system.

The chapter employs gradient-boosting machine (GBM) (“machine learning”) models to sift through the enormous amount of information contained in the simulated worlds to identify the best set of predictors for TDE and AP scores. This knowledge about predictors is combined with what we know about specific elections—for example, the 2013 German federal election—to produce scores for the interparty and intraparty incentives generated by their component rules. The authors leverage a very comprehensive collection of detailed data on real elections held in 140 countries between 1945 and 2015. The database records information on each electoral component used in Chapter 4, and they are used to generate TDE and AP for all the systems used in 1,528 elections.

This chapter tests whether the Total Duvergerian Effect (TDE) explains the size of party systems. It discusses the most widely used measure of party system size—the effective number of parties (N). It not only looks at the simple effects of electoral rules on party system size, but also how those rules operate across constituencies where voters are more-or-less diverse. Increasing TDE is associated with smaller party systems. What is more, as voters grow more diverse, high TDE electoral systems discourage them from supporting as many parties as equally diverse constituencies do under low TDE systems.

This chapter tests whether the Total Duvergerian Effect (TDE) is correlated with the dispersion of party platforms along the Left–Right ideological continuum. The measure of dispersion is based on the Earth Mover’s Distance (EMD) algorithm that considers how far, in a mathematical sense, the distribution of political party locations in a given system is from being “uniform.” The focus is on the array of parties or their presence across some length of the system, not polarization—the presence of major parties only at each extreme of the ideological continuum. The authors find that strong systems, those with high TDE scores, tend to result in parties taking up a limited number of positions on the ideological spectrum while weak systems, those with low TDE scores, lead to parties arraying themselves more evenly across the spectrum.

This chapter examines whether electoral systems affect the degree of correspondence between citizens’ preferences (weighted by their number) and parties’ positions (weighted by their size). It seeks to determine whether a system’s Total Duvergerian Effect (TDE) is related to ideological congruence between citizens and politicians. Using data from Latin America on how citizens’ preferences are distributed and how politicians’ preferences are distributed, the authors conclude that systems with a high TDE tend to be associated with lower levels of many-to-many congruence.

The chapter briefly discusses what the literature says about the relationship between vote-seeking incentives and campaigns, captured with multiple indicators. It uses data from a large, ongoing project—the Comparative Candidate Survey (CCS)—to examine whether what respondents say about the focus of their campaigns is related to the intraparty incentives they face from the electoral systems in which they are competing. The authors find that candidates who face strong personal vote-seeking incentives—systems where Average Personalism (AP) is high—say they put a greater emphasis on themselves as individuals, not their parties as collectives.

This chapter leverages variation across systems in incentives for intraparty politics—as captured by the Average Personalism (AP) measure—to look at the extent to which elected officials report providing constituency service. The chapter reflects on the advantages and disadvantages of different indicators of constituency service. It then focuses on the PARTIREP dataset to construct a set of legislators’ constituency service scores. Empirical tests show that as AP rises legislators are more likely to devote time to providing constituency service. The chapter concludes by making suggestions regarding data collection for those who may be interested in future research on this topic.

The chapter begins with a review of some of the literature that explores the effects of electoral systems on cameral rules and legislative procedures, focusing primarily on the relationship between electoral systems incentives and the number of standing committees in a legislature and between electoral systems incentives and the assignment of legislators to standing committees of different sorts. The authors find support for the idea that where MPs are elected by systems with high Average Personalism (AP) scores, legislative chambers are likely to have a relatively large number of committees. In a second empirical section, they find that where AP scores vary across districts within a system, MPs chosen in districts with higher AP scores will be more likely to be assigned to “pork barrel” or distributive committees.

This chapter explores whether electoral rules that incentivize party members to distinguish themselves from their co–partisans, those with high Average Personalism (AP), affect observed levels of party unity. The authors describe the sources of party unity, making a distinction between having copartisans with shared preferences and the ability to enforce discipline where it might not otherwise occur. They then make the case for why connections through social media are particularly suitable for looking for the effects of electoral incentives. The chapter finds that decisions to amplify in-party/out-party messages by retweeting (or rebroadcasting) them on Twitter (currently known as X) is positively associated with AP.

The chapter opens with a brief review of previous efforts to capture whether elected officials are focused on “pork” or policy. It distinguishes between expert surveys and direct observations of legislators’ efforts and between national-level measures and measures that can be captured at a disaggregated district or legislator level. Using bill initiation data collected by Muñoz-Portillo (2021)—which is a direct observation at the legislator level—for periods before and after an electoral reform in Honduras, the authors find that an increase in Average Personalism (AP) is associated with an increase in pork-barrel politics. The chapter concludes by briefly connecting the authors’ findings using AP to the existing literature on electoral system incentives and particularistic vs. programmatic representation.

The concluding chapter sums up the variety of tasks the authors set for themselves—and successfully completed—in this book. The authors then refocus on the series of contributions made primarily in Part II, including the simulations they developed that allow for the measurement of an electoral system’s interparty incentives—Total Duvergerian Effect—and intraparty incentives—Average Personalism (AP). They then make the case that the approach they have taken and the “goods” they have produced have the potential to serve as the foundation for another push forward in a field of study that many scholars would consider to be mature (or even overripe).