2 International migration estimates
Background
5. International migration estimates produced by
the ONS attempt to reflect how much the UK population has changed
as a result of migration. They estimate how many migrants have
been arriving and leaving, where they are migrating to and from,
and for what reasons. They aim to measure all long-term international
migration to and from the UK, which is migration by people who
change their country of usual residence for a period of at least
a year. ONS migration estimates are the only statistics that attempt
to routinely measure all migration to and from the UK within a
given period using a consistent definition. As migration is a
component of population change, ONS migration estimates are used
in estimating population change in years between the decennial
Censuses.
6. ONS migration estimates are based principally
on the International Passenger Survey (IPS), which is a survey
of passengers arriving at and departing from UK air and sea ports.
The IPS was not primarily designed for the purpose of estimating
international migration, but to provide economic data on travel
and tourism. As most people travelling to and from the UK are
not long-term international migrants, the IPS must approach around
800,000 passengers each year in order to achieve a sample of around
5,000 migrants.[3]
7. The ONS first produces estimates of international
migration using just the IPS sample. These survey-based estimates
are then adjusted to reflect types of long-term migration that
are not properly captured by the survey, such as asylum seekers,
migration through Northern Ireland, and "switchers"—people
who change their country of usual residence for a period longer
or shorter than they originally anticipate, thereby falling into
and out of the definition of a long-term migrant. The adjusted
estimates are the long-term international migration (LTIM) estimates,
which provide the headline estimates of immigration, emigration
and net migration in the UK.[4]
8. The ONS has produced long-term international migration
estimates for each calendar year since 1991, for years to June
since 2003, and for years to March and September since 2010. Figure
1 shows LTIM estimates of immigration, emigration and net migration
in years to December and June since 1991, for those years where
data are available.
Figure 1: Long-term international migration, Years
to Dec & Jun, 1991-2012
Note: Years to June only available since the year
ending June 2003.
Source: ONS, Migration Statistics Quarterly Report,
May 2013
9. Net migration is the difference between immigration
and emigration: the number of people moving to live in a particular
country minus the number of people moving out of that country
to live elsewhere. It is important to recognise that net migration
does not indicate the full extent of population change. If immigration
and emigration are roughly equal, net migration will be low irrespective
of how many people are migrating in and out of the country. Low
net migration can be consistent with high levels of immigration
and emigration, and net migration may change as a result of changes
in either immigration or emigration.
10. Net inward migration to the UK increased from
an annual average of around 37,000 in the period 1991 to 1995
to an annual average of around 209,000 in the period 2006 to 2010.
So while the Government's net migration target—to reduce
net migration from the hundreds of thousands to the tens of thousands—suggests
a ten-fold reduction in net inward migration, in practice net
inward migration only needs to be roughly halved in order for
the Government to achieve its aim.
11. Because the international migration estimates
are based on a survey sample, rather than a count, they are subject
to a margin of error. In practice this error can be quite large.
For net migration (as measured by the unadjusted IPS estimate),
the range is currently around plus or minus 35,000, which means
there is a 95% chance that the true level of net migration falls
within a range of around 70,000. This is called "the confidence
interval" and is calculated by ONS statisticians. Confidence
intervals cannot be calculated for the final adjusted LTIM estimates
because the uncertainty associated with some of the adjustments
cannot be easily quantified, but the confidence intervals surrounding
the IPS estimates give some indication of the statistical uncertainty
in ONS migration statistics. This means that if the estimate of
net migration is, for example, 200,000, the confidence interval
suggests there is a 95% chance the true value falls between 165,000
and 235,000, with a 5% chance the true value falls outside this
range. In practice, the uncertainty is even greater than this,
as the confidence interval only represents the potential sampling
error, and takes no account of other possible sources of error,
such as the possibility of respondents lying or systematic biases
in the willingness of particular groups to participate in the
survey.
12. Figure 2 shows immigration and emigration in
the year to June 2012 broken down by nationality. Just over half
of immigration to the UK is by non-EU nationals (55%), around
a third is by nationals of EU countries other than the UK (30%),
and less than a sixth is by British nationals (15%). This means
that just over half of the immigration flow comprises people who
need a visa to come to the UK. Conversely, most emigration from
the UK is by British nationals (44%), around a third is by non-EU
nationals (32%), and around a quarter is by nationals of other
EU countries (24%).
13. Figure 3 shows net migration by nationality in
years to June from 2003 to 2012. Net immigration is highest among
non-EU nationals, while there has been net emigration of British
nationals in every year since LTIM estimates have been produced.
Because more British nationals are leaving the UK than entering
it, the overall level of net migration is lower than would otherwise
be the case. An increase in net emigration of British nationals
since 2010 has contributed to the fall in net migration during
this period.
Figure 2: Immigration and emigration by nationality,
Year to June 2012
Source: ONS, Migration Statistics Quarterly Report,
May 2013
Figure 3: Net migration by nationality, Years
to June, 2003-2012
Source: ONS, Migration Statistics Quarterly Report,
May 2013
Quality of international migration
estimates
14. In 2009 the UK Statistics Authority (UKSA) carried
out an assessment of ONS migration statistics. It said that "Both
users and ONS' statisticians generally agree that migration statistics
are not fit for all of the purposes for which they are currently
used and require further improvement".[5]
15. Between April 2008 and March 2012 the ONS carried
out a comprehensive programme for improving the quality of its
migration statistics. The Migration Statistics Improvement Programme
(MSIP) led to some improvements in the way migration statistics
are produced and reported.[6]
The ONS told us the migration statistics were "fit for purpose".[7]
16. In written evidence, users of ONS migration statistics
welcomed these improvements, but many remained critical of the
overall quality of the international migration estimates. The
Royal Statistical Society told us:
Despite these recent improvements migration statistics
are still not fully adequate for the task of producing robust
population estimates or understanding patterns of migration.[8]
The British Society of Population Studies wrote:
The statistics on migration to and from the UK
and its constituent parts are inadequate not only for social scientific
inquiry but also for monitoring the effectiveness of measures
designed to implement government policy.[9]
The Royal Geographical Society said "the international
migration data are not fit for purpose", but concluded that
"the ONS (and its sister agencies) are doing a good job with
poor data".[10]
17. The most common criticisms of the migration estimates
were the degree of uncertainty surrounding the statistics and
the lack of detailed information available on the characteristics
and behaviour of migrants entering and leaving the UK.[11]
Both of these problems were attributed to the IPS and its small
migrant sample. The British Society of Population Studies told
us:
[I]t can confidently
be stated that the key problem
with the quality of these migration statistics is the reliance
on the IPS for the main element of the total numbers of immigrants
and emigrants. Therefore the most obvious way of improving their
quality is by reducing the degree of uncertainty surrounding the
IPS-based estimates, which requires greatly increasing the number
of migrants interviewed from its current level of around 12 a
day.[12]
18. Many of those who submitted written evidence
hoped that data from the Government's e-Borders programme—which
records basic travel document information on the identity of passengers
travelling through UK ports—could eventually be used to
improve the quality of migration estimates.[13]
19. The ONS explored the potential use of e-Borders
data as part of the Migration Statistics Improvement Programme.
The biggest contribution they expect e-Borders data to make is
in improving the accuracy of the headline measures of immigration,
emigration and net migration at the national level. This improvement
is expected around 2018, three full years after the e-Borders
scheme achieves 95% coverage of passenger movements in and out
of the UK.[14] This is
because e-Borders data must be collected for a full year before
and after the year for which migration statistics are produced
in order to determine whether a person entering or leaving the
UK meets the definition of a long-term international migrant.
20. However, while e-Borders data may lead to more
accurate headline estimates of immigration, emigration and net
migration, it cannot replace the IPS in providing information
on the characteristics of migrants, as it does not record all
of the characteristics of migrants that the IPS currently records,
such as their usual occupation before migration or their main
reason for migrating. It can also play only a limited role in
helping to improve local area migration estimates as it does not
record the origin or intended destination of people migrating
to and from the UK. We look at this issue further in Chapter 3
below.
21. Users and producers of migration statistics both
said that data on emigration was even weaker than data on immigration.
Several respondents to our call for evidence suggested that emigration
statistics could be improved by using data on immigration in other
countries.[15] The Royal
Statistical Society said:
Estimates of emigration from the UK are known
to be hardest to produce. The potential for use of other countries'
immigration data should be considered to validate the UK estimates.
Furthermore, the Office for National Statistics could proactively
encourage cooperation between member states of international organisations
such as the European Union, OECD and UN to work together on this
issue.[16]
22. In a recent review of the robustness of the International
Passenger Survey, UKSA also recommended using data on international
migration collected in other countries to help understand migration
to and from the UK.[17]
23. We welcome work the ONS has done to improve
the quality of migration statistics. The ONS has done its best
to produce informative migration statistics using the International
Passenger Survey. However, the International Passenger Survey
is inadequate for measuring, managing and understanding the levels
of migration that are now typical in the UK. The Government
must plan to end reliance on the International Passenger Survey
as the primary method of estimating migration: it is not fit for
the purposes to which it is put.
24. e-Borders data has the potential to provide
better headline estimates of immigration, emigration and net migration
from 2018. The ONS and Home Office should move as quickly as
possible to measuring immigration, emigration and net migration
using e-Borders data.
25. Migration is an international phenomenon.
Data held by other countries on migration to and from the UK could
help improve the depth and quality of UK migration statistics.
The ONS should co-operate further with foreign national and
international statistics agencies to improve the quality of UK
migration statistics.
Measuring progress against the
net migration target
26. In written evidence, many users of migration
statistics expressed concern that the degree of uncertainty in
the migration estimates made them unsuitable for measuring progress
against the Government's net migration target. Migration Watch
told us:
The uncertainty around the net migration figure
should be reduced. The net migration figure is central to the
Government's policy on immigration and their success in this area
will be largely judged on this figure. It is therefore far from
ideal that the true net migration figure could deviate
so substantially from the calculated estimate.[18]
The Oxford Migration Observatory wrote:
The available migration estimates are problematic
as a means to define and precisely measure progress toward a numerical
limit on migration [...] For the Government to be judged on its
achievement in delivering this target, accurate measurement is
important. But to know whether this target has been reached requires
clear data—of the sort that the IPS does not currently produce
because of the uncertainty surrounding the estimates. As a consequence,
the Government could miss the "tens of thousands" target
by many tens of thousands and still appear to have hit it—conversely
the Government could hit, or even exceed its target and still
appear to have missed it by tens of thousands.[19]
Submitting evidence in his capacity as Chair of the
Universities UK working group on student visa issues, Professor
Edward Acton said that such uncertainty could lead to immigration
policy that was either too tight or too loose.[20]
27. The only respondent to the Committee's call for
evidence that felt the current migration estimates were adequate
for this purpose was the Migration Advisory Committee (MAC), which
advises the Home Office on migration policy.[21]
However, it is worth noting that the MAC's recommendations to
the Home Office have been influenced by the potential inaccuracy
of the migration estimates. When the MAC was asked to suggest
visa limits to help achieve the net migration target in 2010,
it aimed at reducing net migration to 50,000 rather than 100,000
specifically in order to overcome uncertainty in the net migration
estimate.[22]
28. We wrote to Sir Andrew Dilnot, Chair of UKSA,
to ask whether UKSA considered the LTIM estimate of net migration
to be suitable for measuring progress against the Government's
net migration target. In his response, Sir Andrew wrote:
With careful analysis of all the available data
we can be fairly sure of the broad level of net inward migration
over a period. It may, however, be necessary to wait quite a long
time to get a clear picture.[23]
As illustrated in Figure 1 above, the estimated level
of net migration can change by tens of thousands in either direction
from one calendar year to the next, so medium and long-term trends
in net migration only become apparent after several years. The
true level of net migration at a given point in time is highly
uncertain.
29. In the longer term, migration estimates based
on the International Passenger Survey are too uncertain for accurate
measurement of progress against the Government's net migration
target. We are struck by the advice of the Migration Advisory
Committee to the Government that it should aim for net migration
of only 50,000 as the only means of being certain that net migration
is in fact below 100,000. The Government should not base its
target level of net migration on such an uncertain statistic:
doing so could lead to inappropriate immigration policy.
Understanding who is migrating
to and from the UK
30. The statistical uncertainty associated with migration
estimates increases (relative to the size of the flows) when the
IPS sample is broken down to identify particular sub-groups of
migrants, such as those of a particular nationality, or those
with a particular reason for migration. So, for example, when
the estimate of net inward migration by nationals of the A8 Eastern
European countries that joined the EU in May 2004 is 28,000, the
95% confidence interval surrounding the estimate is around plus
or minus 14,000.[24]
This means there is a 95% chance that the true number of migrants
from those countries falls between 14,000 and 42,000.
31. This statistical uncertainty limits the extent
to which the IPS sample can be broken down into different sub-groups.
Therefore, breakdowns of immigration and emigration by nationality,
country of birth, and country of last or next residence are only
available for groups of countries (such as the EU15, the A8, and
the Old and New Commonwealth) rather than for individual countries.
In its evidence to this Committee, the Royal Statistical Society
said:
Changing patterns of international migration
over recent years—and probably into the future—means
that there is an increasingly wide matrix of countries of interest,
for example the BRIC countries (Brazil, Russia, India and China).
Yet the ONS continues with the same breakdown as in recent decades
(Old and New Commonwealth, Other Foreign, EU etc.).[25]
32. Furthermore, as UKSA indicated in its written
evidence, certain characteristics of migrants are not recorded
by the IPS at all; such as ethnicity, religion, language, and
educational qualifications.[26]
The Royal Statistical Society noted that the absence of data on
ethnicity in particular "makes it difficult to estimate the
impact of international migration on the ethnic composition of
the population, needed for planning of various services such as
education and health".[27]
33. The ONS told us the IPS was not an appropriate
source of data for detailed information on the characteristics
of migrants.[28] It did
not recommend trying to improve the level of detail available
in migration estimates by increasing the size of the IPS, because
even a very large increase in the number of people surveyed would
not provide the level of detail users of migration statistics
need. For this reason, the ONS argued that increasing the IPS
would be "poor value for money".[29]
Instead, it recommended that migration statistics could be improved
more cost-effectively by developing new sources of data on migration,
such as by fully integrating the IPS with e-Borders and by conducting
specific routine surveys of migrants living in the UK.[30]
34. Migration estimates based on the International
Passenger Survey do not provide sufficient detail on the characteristics
of people migrating to and from the UK to judge properly the social
and economic consequences of migration and the effects of immigration
policy. These data are indispensible for anticipating demand for
public services such as schools and the NHS. Migration statistics
should provide detailed information on the characteristics of
people migrating to and from the UK within particular periods,
including information that is relevant to evaluating the impact
of immigration policy and necessary for planning services. The
ONS should broaden the information it gathers on the characteristics
of migrants to include level of educational qualification, labour
market skills, ethnic group, and languages spoken.
35. e-Borders data could potentially provide detailed
information on the characteristics of migrants subject to visa
control. However, e-Borders data alone will not provide detailed
information on the characteristics of those migrants not subject
to visa control, or any information on the geographical origin
and destination of migrants within the UK. If the International
Passenger Survey is not an adequate source for this information,
and no other sources are available, new sources of migration statistics
are needed, even though they may come at some cost.
36. The ONS should develop new sources of data
that can provide accurate statistics on the numbers and characteristics
of people migrating to and from the UK, and on their areas of
residence within the UK. The ONS should link International Passenger
Survey responses to e-Borders data as soon as possible. However,
the need for further data may also require the creation of a new
routine migrant survey covering the whole of the UK.
3 Q 59 Back
4
ONS, Long-Term International Migration Estimates - Methodology
Document - 1991 onwards, May 2013 Back
5
UK Statistics Authority, Assessment Report: Migration Statistics,
July 2009, p 7 Back
6
ONS, Migration Statistics Improvement Programme Final Report,
March 2012 Back
7
Q 59 Back
8
Ev w18 Back
9
Ev w2 Back
10
Ev w1 Back
11
Ev w2, Ev w6, Ev w8, Ev w13, Ev w18 , Ev w27 Back
12
Ev w2 Back
13
Ev w1, Ev w2, Ev w8, Ev w10, Ev w13, Ev w18 Back
14
ONS, Delivering statistical benefits from e-Borders, p
7 Back
15
Ev w2, Ev w18, Ev w31 Back
16
Ev w18 Back
17
UKSA, Monitoring Brief reviewing the robustness of the International
Passenger Survey, June 2013, p 3 Back
18
Ev w8 Back
19
Ev w10 Back
20
Ev w6 Back
21
Ev w8 Back
22
Migration Advisory Committee, Limits for Tier 1 and Tier 2
for 2011/12 and supporting policies, November 2010, paragraphs
45-48, p 12 Back
23
Ev w36 Back
24
The A8 countries are the eight Eastern European countries that
acceded to the European Union in May 2004, comprising Czech Republic,
Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia, and Slovenia. Back
25
Ev w11 Back
26
Ev w31 Back
27
Ev w18 Back
28
Q 59 Back
29
Q 61 Back
30
Q 63 Back
| 
