When people in developing countries worry about migration, they are usually concerned at the prospect of their best and brightest departure to Silicon Valley orto hospitals and universities in the developed world. These are the kind of workers that countries like Britain, Canada and Australia try to attract by using immigration rules that privilege college graduates.

   Lots of studies have found that well-educated people from developing countriesare particularly likely to emigrate. A big survey of Indian households in 2004 found that nearly 40% of emigrants had more than a high-school education, compared with around 3.3% of all Indians over the age of 25. This “brain drain” has long bothered policymakers in poor countries. They fear that it hurts their economies, depriving them of much-needed skilled workers who could have taught at their universities, worked in their hospitals and come up with clever new products for their factories to make.