Facebook reveals number of migrants in the UK has been underestimated

Studying Facebook has helped reveal the number of European migrants in the UK has been underestimated by as much as 25%.

Currently, official migration statistics are collected and reported by the Office of National Statistics. But this new research used other 'digital trace' materials, including the social media platform, to reveal that, in 2018, there were 25% more European migrants in the UK than the ONS statistics suggested and, in 2019, there was an additional 20%.

Data from a range of sources was examined, including Facebook, the Labour Force Survey and country-specific information, to provide a more accurate picture. In 2019, the ONS estimated, there were around 3.6 million European migrants in the UK. But this research suggests the true figure was around 4 million.

The poor quality of the official migration data is the reason for the underestimate. Indeed, the ONS has reclassified the migration estimates as experimental statistics. But what is striking is that our study reveals the underestimate is even bigger than thought. This is important because decisions-makers require accurate evidence-based information to produce effective policies that affect people's lives.

Knowing the number of migrants in a region is important for planning….for example for schools and transport. Knowing the number of people is important for estimating the denominator (how many residents). This has proved very important recently in understanding the number of people vaccinated for COVID-19.

Moreover, it is important to monitor changes in migration policy. The UK has recently changed its policy on European migrations: it is important to understand the effect of `Brexit' on the number of Europeans living in the UK. Digital trace data gives us the opportunity to investigate this change with weekly or daily estimates.

The ONS is aware of an undercount of 16% for net migration to the UK from eight EU countries in 2016. Currently, the UK uses a survey-based system to collect migration information and relies heavily on the International Passenger Survey (IPS), created in 1961 and which the ONS admits 'has been stretched beyond its original purpose."

In comparison, this research combines statistics from The Facebook Advertising Platform, the LFS, and unemployment and GDP (Gross Domestic Product) figures from each of the 20 countries included in the study.

We looked at unemployment and GDP figures for each country to better understand the push and pull factors of migration. Why migrants might move away from their home country or return to it.

This study shows that we cannot trust either data source on its own. Both the LFS and the Facebook data are biased. It is important to combine data sources to have better estimates of migration and measure uncertainty. The ONS is working on updating its migration estimates using administrative data source (i.e. RAPID). We suggest also using digital trace data, to give a better sense of the number of migrants.

The Facebook Advertising Platform provides advertisers with information on the age, sex, language, and real time location data of its users. It can tell where users are accessing the platform, the country they came from, and defines a migrant as a person who used to live in country x and now lives in country y. The Labour Force Survey measures the inflows and outflows of international migrants and collects data every three months. However, migrants tend to come and go—or at least that was the case before the pandemic.

The countries included in the study are Belgium, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, the Netherlands, Poland, Portugal, Romania, Slovakia, Spain, and Sweden.

Information was collected from the Facebook Advertising Platform in the third week of July 2018 and in July in 2019. Data from the Labour Force Survey was provided by the ONS for the period of June–July 2018 and June–July 2019.