An OECD report on international migration states, under the heading "Brain drain: myths and realities", the following:

"An issue that has been attracting a lot of attention is the emigration of people holding tertiary degrees, the so-called “brain drain”. In most of the large countries of origin, such as Brazil, China and India, less than 5% of the highly-skilled emigrate. But for small countries, brain drain can reach substantial proportions. Countries such as Jamaica, Haiti, Mauritius and Fiji, for example, have more than 40% of their highly-skilled people abroad; in some cases, even 80%. And women from developing countries with tertiary degrees are more likely to emigrate to OECD countries than highly-skilled men: 17.6% versus 13.1%.
We have used the database to examine jointly with the WHO how brain drain affects the health sector. We found that, on average, in the year 2000, 11% of nurses and 18% of doctors employed in the OECD area were foreign-born. This is about the same percentage as that of all highly-skilled migrants in the work force. African and Caribbean countries are particularly affected. In some cases, expatriation rates of health professionals reach 50%. This adds to the health workforce challenge that these countries are already facing. But the estimated labour shortage in their health sectors is far greater (almost 8 times higher) than the number of foreign-born health workers in OECD countries. So stopping the flow, if that were possible, would help a bit, but it would not solve the problem.

To be prepared for the future, governments need to act now to put proper policies in place to help satisfy labour needs partly through migration and to enable the integration of migrants. Every OECD country should make this a priority. It is socially, politically, ethically, and morally correct, but it is also an act of sheer economic rationality."

Details at
http://www.oecd.org/document/14/0,3343,en_2649_201185_40125838_1... .