Between 3.9 and 4.8 million unauthorized immigrants resided in Europe in 2017, new estimates from the Pew Research Center show. According to the research, unauthorized immigrants living in European countries reached a peak in 2016 and have been decreasing since then.

The latest total is up from 2014, when between 3.0 and 3.7 million unauthorized migrants lived in Europe, but dropped from the recent peak of 4.1 to 5.3 million in 2016.

Pew Research Center used data from the 28 European Union member states and from four additional European Free Trade Association (EFTA) countries (Iceland, Liechtenstein, Norway and Switzerland), producing the first comprehensive European data in a decade. ‘Unauthorized immigrants’ in this report are all the people living without a residency permit in their country of residence who are not citizens of any European Union or European Free Trade Association (EFTA) state.

The research shows that, even with the growth of the unauthorized immigrant population in EU-EFTA countries since 2014, unauthorized immigrants in 2017 accounted for less than 1% of Europe’s total population of more than 500 million. Also, there were four times as many authorized immigrants as there were unauthorized immigrants.

The highest numbers were registered in the UK (1,200), followed by Germany (700), Italy (600) and France (300). The UK and Germany alone amounted to about half of Europe’s total and these top four countries had more than two-thirds of Europe’s total.

According to the Center, the recent rise in Europe’s long-standing unauthorized immigrant population is largely due to a surge of asylum-seekers who mostly arrived in 2015 . So, in 2017, asylum-seekers in Europe still awaiting a decision on their application accounted for roughly a quarter (20% to 24%) of the unauthorized immigrant population.

“The surge of asylum seekers contributed to a higher number of unauthorized immigrants in many European countries,” said Senior Researcher Phillip Connor, the lead author of the report. “But unauthorized immigrants also include those who overstayed a visa or entered Europe illegally, many of whom migrated years ago.”

Details about the origin of the immigrant population show that about 33% of them were from Asia-Pacific countries, 21% from countries in the Middle East-North Africa region, 17% from sub-Saharan African countries and 8% from countries in the Americas.

In 2017, 56% of unauthorized immigrants in Europe had lived there less than five years and about two-thirds of the unauthorized immigrants residing in Europe were younger than 35 years old.