It’s intuitively obvious: if you allow more people to migrate to wealthy countries, global poverty rates will come down because people will have more and better labor opportunities. Conversely, immigration restrictions keep poverty levels high. Here‘s a paper that actually tries to measure the effect on poverty of migration restrictions:
[R]ich nation migration barriers impose huge losses on the global economy. This paper … estimates, for the first time to my knowledge, the global poverty implications of those barriers and finds that freeing migration into rich nations would reduce global poverty by at least 40% and as much as 66%. This corroborates the conclusions drawn by others that opening rich nations to freer migration may do more to reduce poverty around the world than any other policy.
Another study finds similar results:
[O]pen borders could yield huge welfare gains: more than $10,000 a year for a randomly selected worker from a less-developed country (including nonmigrants). Another is that these gains are associated with a relatively small reduction in the real wage in developed countries.
More posts in this series are here.