• James Urton-Washington

A new estimate suggests global migration is much higher than we thought

Researchers have unveiled a new statistical method for estimating migration flows between countries, using the so-called pseudo-Bayes approach.

They show that rates of migration—defined as an international move followed by a stay of at least one year—are higher than previously thought, but also relatively stable, fluctuating between 1.1 and 1.3 percent of global population from 1990 to 2015.

In addition, since 1990 approximately 45 percent of migrants have returned to their home countries, a much higher estimate than other methods.

Migration is much more than the place you left and the place you ultimately settled in.

On today’s increasingly crowded globe, human migration can strain infrastructure and resources. Accurate data on migration flows could help governments plan for and respond to immigrants. Yet these figures, when available, tend to be spotty and error-ridden, even in the developed world. Researchers have developed approaches to estimate migration rates, but even the best of these rely on unrealistic assumptions about the mass movement of people and yield migration rates that can fall far below reality.

The researchers report their work in the Proceedings of the National Academy of Sciences. The more accurate estimates of migration will ultimately help both migrants and the people who assist them, says senior author Adrian Raftery, professor of statistics and sociology at the University of Washington.

“Planning for migration is no simple task,” says Raftery. “You need everything from medical infrastructure and trained personnel to elementary schools—and governments rely on accurate demographic estimates to help them put the right plans and responses into place.”

A better estimate

Countries collect migration data through immigration forms at ports of entry, but answers on these forms may contain mistakes, and often fail to collect the types of comprehensive information that demographers need to measure migration accurately. Census forms also tend to ask people where they were born, but usually not when they moved, information which does not accurately reflect the true level of movement.

“Migration is much more than the place you left and the place you ultimately settled in,” says Raftery.

“Researchers have tried for years to develop statistical methods that capture the comprehensive picture of human migration across the globe.”

Raftery developed these new migration rate estimates with former doctoral student Jonathan Azose, an affiliate assistant professor of statistics and the paper’s lead author. They applied the pseudo-Bayes method to migration estimates by incorporating elements of other methods, and calibrated their estimates against a relatively reliable model of migration among 31 European countries.

Azose and Raftery tested the accuracy of pseudo-Bayes against a set of reliable migration figures and discovered that its estimates were typically accurate to within a factor of three, better than many existing estimates.

“For the migration field, this level of accuracy is a significant improvement,” says Azose. “Even when you look at data from European countries, it’s not uncommon for a single migration flow to have estimates that differ by a factor of three or more depending on whether the sending or the receiving country collected the data.”

They also discovered that, compared to other approaches, pseudo-Bayes can more accurately account for return migration, in which migrants go back to their home countries.

“Our estimate shows a higher global flow of migrants in large part because it indicates that return migration is much higher than previously thought,” says Azose.

Courtesy : World Economic Forum