1 Million Missing Immigrants (And 1.2 Million More UK-Born)

A new Kings College post by Michael O'Connor highlighted the strange case of a rapid fall of around 750,000 in the immigrant population of working age over the last year contained inthe latest ONS labour market statistics . This is very remarkable indeed.

It is all the remarkable still, when one realises that the same survey on which these numbers are based - the Labour Force Survey (LFS) - also shows a fall in the total immigrant population (age 0 upward) of 1 million between 2019 q4 and 2020 q3 AND a rise in the UK-born population of 1.25 million over the same period.

To see how unusual these changes in population are, take a look at the Figures below. Figure 1, left panel, shows the immigrant population (defined as born outside the UK) since 2007.¹ Immigration usually falls a little in recessions. Fewer job opportunities reduce the incentive to come to the UK. Job losses encourage some migrants to leave the UK to seek better fortune elsewhere. During the 2008-2011 downturn there was a little wobble in the immigrant population, but not much to alter the longstanding upward trend in immigration that began in 1995. There were larger falls in the immigrant population after Brexit. But nothing compares to the size of the fall that appears to have gone on during the 9 months of the COVID crisis.

Not only this, the UK-Born population appears to have jumped by around 1.2 million over the same period. This is remarkable indeed. No such period of rapid population growth can be observed in the last 15 years.

Figure 1. UK-Born and Immigrant Populations in the UK 2007-2020 Figure 2 graphs the same data but using the yearly change to get a sense of how unusual these developments are. The yearly growth in the UK-born population was averaging around 350,000 a year prior to 2019 and then...kapow.
The overseas born population was growing at a slighty larger rate and the comes Brexit and then.. kapow.
Figure 2. Yearly Change in the UK-Born and Immigrant Populations in the UK 2007-2020

Figure 3 breaks down the Overseas and UK-born population changes by 10 year age bands.² You can see upticks in the growth of several of the UK-born groups eg. 41-50 after the end of 2019. And downturns in the overseas-born age groups eg 31-40 What is even odder is that if we align these age groups, then the population of UK-born 31-40 year olds ten years ago should equal the population of 41-50 year olds now, give or take some deaths and emigration. A 30 year-old in 2010 is a 40 year old now. Figure 4 plots the actual and predicted population of UK-born 41-50 year olds over time. The lines generally run paralell. The prediction is above the actual population, as expected, but it is paralell - until the start of 2020 when they suddenly diverge.
Figure 4. Predicted and Actual Age Cohort Populations: UK-Born Age 41-50 2017-2020

So something really unusual is going on. It may be that the COVID crisis has simultaneously reduced migrant inflows and increased outflows by an unprecedented amount while at the same time uncovering a new strata of the UK-born population. Or it may be something lurking in the LFS to do with sampling of households over the crisis and the subsequent impact on the population weights.³ Indeed the two issues are related. Stay with this, it gets slightly esoteric for the next two sentences.

The LFS sample numbers are grossed up to the Census projections for the total UK population in each year. If the LFS picks up a decline in immigrants in its sample but the census population projection is unchanged, then the LFS weights will inflate the UK-born population to compensate for the missing immigrants. Got that? The ONS believes that its huge fall in immigrant numbers picked up in the sampling is real. But the Census projection for the total population in 2020 remains unchanged. As such the automatic rebalancing in the weights kicks in. So that explains why the UK-born population grows quite rapidly in 2007/18 in Figure 2 above -a period when it seemed the immigrant population was falling after Brexit. It also explains why the estimated UK-born population takes off into the stratosphere in 2020 in Figure 20. So the population of UK-born individuals is almost certainly off. We will look into how much this affects labour market statistics in future posts. But all this probably demands more attention.

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1 ^↩The LFS data contain population grossing weights that allow the sample to be grossed up to the population. The Figures are all compiled using the grossing weights supplied by the LFS.
2 ^↩So Age 10 is 0-10 years; 20 is 11-20 years etc
3 ^↩The ONS has acknowledged that a re-weighting process to deal with changing responses to the LFS during the crisis is underway