When Wizz Air screwed up immigration statistics

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You’d think it would be hard to lose half a million people, but the Office for National Statistics (ONS) has managed it anyway. Awareness of this problem emerged just over a decade ago when the results of the 2011 census were released. The census revealed that there were nearly five million foreign nationals in the country, 464,000 more than the public thought. ONS. Why hadn’t anyone noticed?

One school of thought blames a Hungarian entrepreneur called József Váradi. Váradi has done nothing wrong, to be clear, but he has participated in a chain of events that has wrong-footed the ONS.

In 2003, Váradi co-founded Wizza Aira budget airline that followed the established pattern of flying people cheap to smaller regional airports.

Not long after, Hungary, the Czech Republic, Poland and seven other countries joined the EU, giving their citizens the right to live and work anywhere in the Union. Many of them decided to settle in the UK and thanks to Wizz Air they often arrived at airports such as Leeds or Luton.

This was good news for anyone looking to hire workers in the UK, but it proved the downfall of the International Passenger Survey (IPS), the mainstay of UK immigration and emigration estimates for many years. IPS is a bit like an opinion poll: IPS inspectors politely stop a sample of people at ports and airports and ask them if they would be willing to answer a few questions. (Surprisingly, almost everyone agrees.)

These questions range from “How much did your plane ticket cost?” to “How long are you going to stay?” Many of the IPS questions are actually about tourism, but the survey generated enough data to estimate migration into and out of the country. . . as soon as. The problem, explains Georgina Sturge in her excellent book Incorrect data, is that while hundreds of thousands of people are interviewed for IPS, most of them are tourists and only a few thousand are migrants. The number for a particular country will often be lowercase.

It’s dangerous enough to extrapolate from this small sample, but what really confuses any survey is an unnoticed change that transforms the sample from fairly representative of the base population to not representative at all. Wizz Air made that change unnoticed. To simplify a bit, IPS enumerators were located in Heathrow, Gatwick and Manchester, while people eager to start a new life in Britain arrived in Luton.

Pro-Brexit activists were quick to highlight the problem, as Sturge explains. Not only could we not control immigration, they said, we could not even count it. But that’s not entirely correct. We could have counted it. But we decided not to.

“Choosing to use a survey over other data is increasingly just that—a choice,” says Anna Powell-Smith, director of the Center for Public Data, a nonprofit campaign for better data and statistics. There are now other ways to produce migration data, or indeed most of the statistics we see all around us in the news or in political discussions.

An alternative would be to require newcomers to register, as they do in Germany, before they have access to basic services such as a bank account or a doctor. There are pros and cons to this idea, but as Sturge notes, “Germany has a better understanding of its immigration statistics despite not having border controls with 25 other European countries.”

The ONS is powerless to introduce such a requirement, but in the wake of the pandemic it has moved from estimating migration with IPS-broad sampling to using administrative data that aims to track every immigrant. This includes now common visas and information from the tax and benefit systems. (Thankfully, there are privacy protections built into how the ONS uses this information.) The first such estimates were produced in May 2022, and IPS is now only used to estimate the comings and goings of UK citizens .

There will be no more Wizz Air-induced statistical errors, says Jen Woolford, director of population statistics at ONS, adding: “If the exact situation were today, it would have no impact on the accuracy of our figures.” It’s good to hear that.

The point is not that we should introduce identity cards. It’s that both Westminster lawmakers and the wonderful nerds at the Government Statistics Service are making choices about what to count and how to count it. Those choices matter, and they could be different if our priorities were different.

As is often the case, we ordinary civilians notice statistical and administrative infrastructure in the same situations we notice sewage or the electricity supply: when something has gone wrong, or some new challenge is testing the system to destruction. The Wizz Air affair was an important example. The race to create a Covid-19 testing capacity was another. The decision to destroy the arrival logs of the “Wind generation” – based on the untested assumption that those documents were superfluous or redundant – was a third party. (It was a reminder that archivists are as much taken for granted as statisticians, perhaps even more so.)

Can we do better? No doubt. Nerdland contains all sorts of ideas, from better estimates of gambling harm, to research environments for reliable health data that can prevent a privacy apocalypse while saving more lives.

But to free those ideas we have to take the data seriously. Much of the data discourse focuses on misleading presentation rather than where the data itself comes from. It’s true, of course, that misleading labels on a graphic or slogan on a bus can be misleading. But statistical work that is underpowered, underfunded, and undervalued can do it, too.

Tim Harford’s children’s book, “The Truth Detective” (Wren & Rook), is now available

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