Migration – uncertainties and other things about the estimates

The Prime Minister gave a long awaited speech on 28 November 2014 on immigration.

Fact-checking organisation, Full Fact, were invited onto Jeremy Vine’s show on BBC Radio 2 that day to explain the facts and figures behind the PM’s speech. For the time being you can listen to it on the web – Full Fact’s contribution is about 17 minutes in. They’ve followed up with answers to the questions put to them. Another article looks at the numbers in the PM’s speech specifically.

I thought it worth adding a bit more to what Full Fact set out – particularly with regard to the uncertainties in the estimates and the difference between country from which a person arrives and their nationality.

The first thing to know is that migration figures don’t come from an exact count of who’s leaving the UK and who’s coming in. Instead, the Office for National Statistics (ONS) carries out a survey – the International Passenger Survey (IPS). They interview between 700,000 and 800,000 people every year. Around 250,000 of these are used for estimates for overseas travel and tourism. As well as the ONS explanations, the Migration Observatory at the University of Oxford has a good article on the IPS.

Full Fact were first asked about the 260,000 migration figure that has made the headlines. As they say, this is a figure for net migration to the UK – the difference between those coming in (immigration numbers) and those going out (emigration numbers). The numbers exclude those just coming in or going out for a short time.

I think it’s useful to point out the uncertainty in this figure. ONS give what is called a 95% confidence interval of plus or minus 39,000. In other words we can be pretty confident that the true figure for net migration is between a number 39,000 less than 260,000 and 39,000 greater – or between 221,000 and 299,000.

The number for those coming into the UK is estimated at 583,000. There is also a confidence interval – of plus or minus 32,000. In other words, the true figure for immigration is likely to be between 551,000 and 615,000.

And for those leaving the UK the estimate is 323,000, with a confidence interval of plus or minus 22,000. So the true figure for emigration is likely to be between 301,000 and 345,000.

Those are big ranges and reflect how difficult it is to count something as big as the numbers leaving for a long time and coming in for a long time. Bear in mind there are also many millions coming and going just for business or tourism. And, these are provisional figures!

Full Fact were also asked where immigrants were coming from. They gave the figures of 33,000 for Spain, 27,000 for Poland and 33,000 for India. These come from final figures for 2013.

Given the big uncertainties in the overall figures you won’t be surprised that there is considerable uncertainty to these figures as well. Here they are:

Estimate +/-CI            Range
Spain        33,000        11,000 22,000 – 44,000
India        33,000          5,000 28,000 – 38,000
Poland        27,000          7,000 20,000 – 34,000

The sources are ONS data tables for immigration and emigration – both in XLS format and selecting the 2013 sheet.

Although the estimates for Spain and India are the same (33,000), the confidence interval for India is smaller. This is presumably because Spain is in the EU (with free movement) and India is not.

This isn’t the end of the story, though. As the ONS point out:

“Country of last residence will not necessarily reflect nationality. For example, around 27% of immigrants arriving from Spain … were British citizens in 2013, while the proportions of those arriving from … India (3%) and Poland (0%) who were British citizens were very small.”

So of the estimated 33,000 (plus or minus 11,000) immigrants from Spain, a little over a quarter are estimated as being UK citizens returning to this country.

The same sort of thing goes for emigration. For example, of those emigrating to Spain somewhat over half (56 per cent) are UK citizens.

NB I’ve done my best to understand the official statistics. But I would always recommend people go to the official source to get the numbers and the explanations that go with them.