The Washington PostDemocracy Dies in Darkness

How statisticians uncovered the world’s missing migrants

Estimating the true number of migrants that move around the world each year is a difficult task -- some people cross borders illegally, and recording and enforcement standards vary a lot by country. As a result, data on international migration is often incomplete. The U.S. may note an increase in foreign-born people across two time periods, for example, but other countries have no parallel record of them leaving.

To fill this gap, Nikola Sander, Guy Abel and Ramon Bauer of the Wittgenstein Centre for Demography and Global Human Capital used statistical missing data methods to analyze the global flow of migrants. Using data on the changes in migrant stock over time, they estimate the five-year flows that are required to account for the differences in the data. The graphic below shows the results for 2005-2010 for the top 50 sending and receiving countries.

Here’s how to read the graphic: Each country is assigned a color. The arcs across the circle, which represent flows of migrants, have the same color as their country of origin. For each flow, the authors left a gap at the destination country, but no gap at the country of origin. The width of the flow indicates its size, while tick marks indicate gross migration (in + out of a country) in 100,000 people.

The graphic offers some pretty amazing insights into the global flows of people. A large yellow band near the top of the graphic shows the nearly 2 million Mexicans that immigrated the US between 2005 and 2010. The graphic also shows substantial flows from China, India and the Philippines into the US. Those who emigrated from the US, on the other hand, were most likely to go to European countries.

The graphic also tracks fascinating flows in other parts of the world: Countries like the United Arab Emirates, Saudi Arabia, Qatar and Bangladesh claim outsized portions of the graphic for their populations. For example, note the huge flow of migrants from India, Pakistan, Bangladesh, Indonesia and the Philippines into the UAE, Saudi Arabia and Qatar, which have a high demand for guest workers.

If you like this graphic, it's worth checking out the interactive version, which lets you click on a region to see the country-by-country flows, as well as look at data for different time periods.

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