There is a large body of evidence indicating that cross-country differences in income levels are associated with differences in productivity. If workers are much more productive in one country than in another, restrictions on immigration lead to large efficiency losses. The paper quantifies...

Most developed countries have foreign aid programs that aim to alleviate poverty and foster economic growth in less developed countries, but with very limited success. A large body of evidence indicates that the root of the economic development problem is cross-country differences in the...