How do face-to-face, assembly processes, and non-face-to-face, popular vote processes impact the decisions made by citizens? Normative discussions of the comparative merits of these two broad types of participatory decision-making processes partly rely on empirical assumptions concerning this question. In this paper, we test the central assumption that assemblies lead to decisions that are more widely supported by participants than popular votes. We do so by analyzing 1,400 decisions made through these processes on the highly salient issue of municipal mergers in Swiss municipalities since 1999. We find that assembly decisions are consistently made by larger majorities than popular vote decisions and that this relationship is significantly mediated by turnout. This suggests that higher levels of agreement in assemblies mainly result from selection biases – with fewer dissenting citizens participating in assemblies than in popular votes – rather than from internal dynamics in assemblies.