[andersriutta]

From the study: "[I]t is possible that migration flows could be a potential mechanism behind this effect. ... However, we do note that we found evidence against a migration explanation in Study 2."

But Study 2 appears to have actually looked at the relationship between GDP per capita (on a country-level basis) and number of international friends per capita (again on a country-level basis). GDP per capita between countries seems like a poor proxy for social class between people within the same society. Even if people in rich countries have fewer international friends than do people in poor countries, does that really indicate my rich neighbor is likely to have fewer international friends than does my poor neighbor?

Edit: looks like zopppo already pointed out this issue before I refreshed.