The number of people migrating to developed countries fell last year for the first time since 2011, but remained near record levels and is unlikely to fall by much over coming years, according to the Organization for Economic Cooperation and Development.
In its annual report on the movement of people across national borders, the Paris-based research body also said the number of illegal immigrants is a much lower share of the total than is commonly perceived, although it acknowledged that reliable figures are hard to come by.
The report comes as governments in the U.S. and Europe face criticism for their immigration policies. German Chancellor Angela Merkel’s coalition government is under threat over plans by a key ally to start turning back some migrants at the border. In the U.S., President Donald Trump faces widespread condemnation for a policy that has separated thousands of migrant children from their parents.
The OECD, which has advised member governments including the U.S. on immigration policy for half a century, said it was worried that recent debates on the subject aren’t being informed by established facts, and that native populations have an exaggerated sense of the scale of migrant flows.
“There is a very serious problem of communication,” said Ángel Gurria, the OECD’s secretary-general. “What we’re seeing is that the numbers are pretty modest.”
Mr. Gurria was critical of the European Union, identifying a recent controversy over the destination of a rescue ship as a sign that “there isn’t a policy” behind the bloc’s treatment of refugees.
And he also spoke out against the U.S. government’s child separation program, saying it broke with the established practice among OECD members of privileging the interest of minors.
“In this case, separation is certainly not in the best interests of the minor,” he said in a news conference. “State security and basic humanity are not incompatible.”
The research body said more than five million people legally crossed borders in 2017, a 5% decline on the previous year. However, that fall was almost entirely because of the end of a surge of refugees into Germany, and the body doesn’t expect flows to fall much over coming years given the differences in rates of population growth and standards of living between developed and developing countries.
“Migration flows have been rising over the past few decades and are unlikely to fall from their current levels, given the large demographic and economic imbalances,” said Stefano Scarpetta, the OECD’s director for employment.
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The OECD recorded that the U.S. remained the most popular destination country for migrants in 2016, the most recent year for which comparable figures are available, taking in 1.2 million of the 5.3 million total. But in that year Germany recorded by far the largest increase, taking in around 1 million new migrants, although some of that reflected the legalization of arrivals that took place in the previous year. The U.K. was a distant third, taking in 350,000 arrivals.
The research body said immigrants shouldn’t squeeze people already in those countries out of jobs or lower their incomes, since they account for a very small share of the potential workforce. It estimates that in Europe, the recent surge in refugees would increase the working-age population by just 0.4% by 2020, and the number of people actually looking for work by just 0.25%.
But it acknowledged that impact will be slightly larger in those countries that have taken the bulk of those refugees, and that a particular group of workers is especially vulnerable.
“The impact is likely to be much larger in specific segments of the labor market, notably among young low-educated men,” it said. “Since this population group is already vulnerable in most host countries, well-targeted measures are needed to provide them with adequate support.”
The research body said a lack of good information about levels of illegal immigration has helped fuel public worries about movements of people across borders.
“Almost half of the European population has the misperception that there are at least as many immigrants staying illegally as legally in Europe,” said Mr. Scarpetta. “Most of them believe there are even more migrants illegally staying than those legally staying, whereas no OECD country even remotely approaches these proportions.”
The OECD estimates that there were roughly 11.3 million illegal immigrants in the U.S. in 2016, equivalent to 3.5% of the total population. It estimates that in 2008, the equivalent figure for the European Union was between 1.8 million and 3.9 million, or 0.4% to 0.8% of the total population. It believes that figure has risen over the past decade.
Write to Paul Hannon at paul.hannon@wsj.com