The overall number of high-skilled migrants to OECD countries increased by 120% from 12 million in 1990 to 27 million in 2010. Most OECD destination countries show greater skill selection in 2010 than 1990. The immigration policies of many destination countries are becoming increasingly selective (e.g., de Haas et al. 2014). For example, we see that Canada is consistently selective, while the United Kingdom demonstrates the largest increase in selectivity. The United States is a notable exception, along with Italy, Portugal, and New Zealand.
The emigration rates of college-educated individuals are always greater than their lesser-educated compatriots across all countries and at every level of development. Why?
First, high-skilled people are more likely to be endowed with skills that are both in demand and globally transferrable. They are able to obtain job offers in advance of emigrating and clearing migration policy hurdles that favor higher levels of human capital. If they are using other migration channels (such as family preferences or lotteries), they know they will find employment or assimilate more easily upon their arrival. In addition, high-skilled migrants generally integrate into the host societies more easily as they are more likely to have better linguistic and cultural as well as professional knowledge of the destination society.
They have better access to global information sources through their social and professional networks. They can better access financial resources and credit. As a result, they are able to meet the financial costs of migration more easily. The highest skilled emigration rates are observed from middle income countries.
This report shows that 20%-50% of migrants leave within five years of arrival, with some variability by country pair and time period. High-skilled migrants appear more likely to leave than low-skilled migrants. At the very highest skill levels, return rates from the United States become substantially lower.
A migrant is defined as high-skilled if he or she has completed at least one year of tertiary education.
From here.