In Outside the Bubble: Social Media and Political Participation in Western Democracies, Cristian Vaccari and Augusto Valeriani provide a welcome intervention into contemporary discussions of social media’s political effects. Drawing from an impressive data set collected in nine different countries over three years—and covering over one-third of total social media users living in democracies worldwide—the authors make a convincing case that social media do have a positive (though, perhaps, limited) effect on political participation and that they do so by “broadening the pool of participants” in political life. The authors also show that that these effects are context-dependent, “shaped by political institutions” that vary across countries (14).

But Vaccari and Valeriani’s contribution goes beyond this substantive argument, with broader implications for how social media research is conducted. For one, the book’s focus is not on platforms’ affordances but rather on their effects on users—which, the authors note, often run counter to what we might expect. Just because we can curate some things on Facebook does not mean we will control everything; “selectivity of sources and networks,” as it turns out, “does not necessarily mean active sel