About 1.4 million refugees and irregular migrants arrived in Europe in 2015 and 2016. We model how refugees and irregular migrants are self-selected. Using unique datasets from the International Organization for Migration and Gallup World Polls, we provide the first large-scale evidence on...

The former EU president Jean-Claude Junker has proposed that all countries of the European Union should also adopt the euro as their currency and recent research has shown that countries currently pursuing this goal indeed fulfill the classical Optimal Currency Area (OCA) criterion of positively...

Canonical models of crime emphasize economic incentives. Yet, causal evidence of sorting into criminal occupations in response to individual-level variation in incentives is limited. We link administrative socioeconomic microdata with the universe of arrests in Medellín over a decade. We...

Gangs govern millions worldwide. Why rule? And how do they respond to states? Many argue that criminal rule provides protection when states do not, and that increasing state services could crowd gangs out. We began by interviewing leaders from 30 criminal groups in Medellin. The conventional...

The Ku Klux Klan reached its heyday in the mid-1920s, claiming millions of members. In this paper, we analyze the 1920s Klan, those who joined it, and the social and political impact that it had. We utilize a wide range of newly discovered data sources including information from Klan membership...

Why does illegal trade often flourish without formal enforcement, but sometimes fail? Why do illegal trade-reducing policies often fail? Why do States often appear to tolerate illegal trade? A model of trade with cops and robbers provides answers. `Safety in numbers' is a key element: the...