There’s substantial evidence that the arrival of refugees from outside Europe will be less beneficial than the influx of skilled immigrants from within Europe. The 2014 U.K. study, for example, showed non-European immigrants lagging behind European immigrants in terms of net contributions. “We know that EU immigrants are on average better educated than non-EU citizens and that high-skilled immigrants have a strong positive fiscal impact, which is not the case for low-skilled immigrants,” said Krieger. On top of that, refugees need food and shelter upon arrival, and often lack immigration papers, among other things. Even so, during some years examined in the U.K. study, non-European immigrants still beat out natives in terms of net contributions.

All these studies suggest that, humanitarian and social-policy concerns aside, certain types of economies are well-positioned to turn immigration flows into profit. Bonin argued, for example, that Germany has benefitted from immigration more than some of its neighbors primarily because of three factors: first, Germany’s labor-hungry economy; second, the relatively high level of integration immigrants achieve in German society; and third, Germany’s relatively large pension system (which means immigrants’ pension contributions are disproportionately valuable). Countries that urgently need workers and pension contributions, therefore, might receive a boost even from lower-skilled immigrants—especially if governments invest in the education and integration of new arrivals. Bonin, for instance, based his estimate for the profitability of immigration in Germany in part on the assumption that at least 30 percent of immigrant children wind up performing, in terms of their career trajectory, on par with native German children. For that, you need them to acquire language skills quickly, integrate to a certain extent with the local population, and experience a certain degree of upward mobility.

In a world where the refugee crisis has made immigration not just an economic issue but a moral one, this question of integration might just be the most important of them all.