“…Second, historical work is more likely to measure the flow of new migrants into the US using passenger lists, whereas the contemporary literature often analyzes the stock of immigrants observed in the US Census at a point in time (e.g., Chiquiar and Hanson, 2005). These two methods need not produce the same answer if return migration is also selective (existing evidence suggests that this is the case; see, for example, Lubotsky, 2007; Abramitzky, Boustan and Eriksson, 2014; Ward, 2015). …”