A substantial body of research explores how individuals make voting decisions. Building on classic studies, most scholarship to date presents voting as atomistic: individuals independently learn about candidates and choose between them based on their personal attributes, beliefs, and preferences. Voters, however, do not acquire information and make decisions in a vacuum. In Persuasive Peers, Andy Baker, Barry Ames, and Lúcio Rennó contend that voters learn about politics through informal discussions with peers and claim that those discussions influence vote choice. They deftly test their theory of socially informed voting and explore the political implications of horizontal intermediation in Latin America. This innovative and informative book elucidates how political discussions within informal social networks shape political outcomes.

In the first part of the book, Baker, Ames, and Rennó introduce their theory of socially informed voting. They contend that in Latin America trusted, politically knowledgeable individuals are “persuasive peers” who can induce their social contacts to vote differently than they would have otherwise. In other words, informal political discussions with family, friends, and colleagues shape voting decisions. In the second part of the book, the authors put this theory to the test. Drawing on interviews and unique surveys of Brazilian and Mexican voters, they demonstrate that conversations with agreeing discussion partners reinforce voting intentions, whereas conversations with disagreeing partners tend to induce preference change. Building on these results, they show that their theory of political communication explains geographic voting patterns in neighborhoods, cities, and regions. Finally, the third part of the book explores how persuasive peers affect the quality and equity of political voice. Specifically, Baker, Ames, and Rennó examine whether clientelistic party machines target persuasive peers and assess how peer influence affects the political voice of marginalized citizens. With respect to clientelism, their analysis shows that party elites do not just buy votes but also purchase influence by targeting well-connected opinion leaders. With regard to the quality of political voice, they find that members of traditionally marginalized groups, such as the poor, do not engage in informal conversations about politics as frequently as the rich and often end up supporting candidates who do not share their attitudes and policy preferences.

Research on Latin America has historically paid little attention to the impact of peer discussions on political behavior. Persuasive Peers convincingly shows that this historically overlooked form of communication is a critical source of political information and influence. In Latin American democracies, voters routinely talk about politics, and when they do, they seek out their politically informed peers. Importantly, voters’ politically knowledgeable peers do not always agree with them about which candidate or political party is best. Peer discussion networks in Latin America are more diverse than those found in the United States. As a result, voters often discuss politics with individuals who support other presidential candidates. Baker, Ames, and Rennó capitalize on this heterogeneity in their analysis of campaign volatility.

Persuasive Peers contributes to the growing literature in political science on networks. Readers, however, do not need to be familiar with social network theories or measures to follow their analyses. The authors couple their hypotheses with quotes from interviewees and informative sociograms. Chapter 4, which includes the book’s core empirical analysis, makes use of an impressive set of original panel surveys from Brazilian and Mexican presidential elections that include repeated measures of egonets. Consistent with the theory, their results indicate that disagreement within peer networks substantially increases the probability that voters change their vote intention. Moreover, Baker, Ames, and Rennó show that the diversity of those disagreeing peers is consequential. When a voter’s discussion partners disagree with each other, the probability that the voter changes their vote intention is lower than when their peers agree with one another. Through a series of robustness checks, they demonstrate that reverse causation, latent homophily, and environmental confounding do not explain their results.

There is reason to suspect that the impact of peers on vote choice that the authors document in presidential elections is even more pronounced in less high-profile contests. In congressional and local elections in Latin America, voters are likely to be relatively uninformed about candidates and therefore turn to their more knowledgeable peers for guidance. Readers do not need to imagine how voters in Brazilian congressional elections, which routinely have more than one thousand candidates, would draw on their peers for political information. In the concluding chapter, a set of WhatsApp messages received by one of the book’s interviewees is included. It illustrates that politically uninformed voters do turn to their peers for guidance when they do not know whom to support.

The WhatsApp messages also point to one mode of communication—online communication—that receives limited attention in the book. Throughout Persuasive Peers, online political conversations are treated as a subset of horizontal political discussions. The authors assert that they “lose little by ignoring the distinction between online and offline discussion” (p. 45). Nonetheless, they acknowledge in the concluding chapter that the effects they uncover may differ in magnitude online. This is important considering the growing use of the internet in Latin America. In the 2018 elections, WhatsApp groups were one of the principal ways that voters shared political information and opinions. Moreover, because of the COVID-19 pandemic, there is reason to suspect that informal political discussions that historically occurred face to face may increasingly take place online.

Within the context of any one book, it would be unrealistic to cover both face-to-face and online discussion. The impact of online discussion on political behavior in less-institutionalized democracies, however, certainly warrants attention. Insight from Persuasive Peers can serve as a starting point for the study of online communication in Latin American democracies. After all, the phenomena that social network and communication scholars are interested in, such as the spread of misinformation, occurred in face-to-face networks long before the creation of the internet.

Online discussion networks may be especially consequential for shaping the voting decisions of traditionally marginalized voters. Baker, Ames, and Rennó find that members of traditionally marginalized groups, such as poor and low-educated voters, are less likely to engage in political discussion and have smaller political discussion networks than rich and well-educated voters. The internet may provide less informed voters access to larger, more informed discussion networks and thereby the means to use their voices more effectively. Yet, not everyone whom voters engage with may provide them information that helps them vote according to their interests. If uninformed voters from marginalized groups have difficulty detecting misinformation and share it themselves, their political voice may be further distorted. In sum, Persuasive Peers demonstrates that informal discussions influence voter behavior but not always for the better.