72. Estimates of international migration used in
the mid-year population estimates are based on the United Nations
definition of a long-term migrant: someone who moves to a country
other than that of his or her usual residence for a period of
at least a year (12 months), so that the country of destination
effectively becomes his or her new country of usual residence.
From the perspective of the country of departure the person will
be a long-term emigrant and from that of the country of arrival
the person will be a long-term immigrant.
73. Short-term international migrants are not included
in the usually resident mid-year population estimates. The Sub-Committee
received written evidence from a number of statistics users stating
that the 'usually resident' definition of population did
not fully meet their needs because short-term international migrants
were not included.
74. The Statistics Commission stated:
Short-term migration is important as it is not normally
included in the official figures for migrants (which, following
international practice, only counts as 'migrants' those intending
to stay for more than a year). But, perhaps particularly following
EU enlargement, short-term migration has the potentialand
already the reality in some areasto have significant implications
for local services. 
The Local Government Association reported that there
was widespread concern among Local Authorities that the official
population estimates did not reflect experience at local level.
A particular difficulty with the usually resident
definition concerns the treatment of migrants. The current system
only counts those migrants who state the intention to remain in
the UK for at least 12 months at the time of entry. There is considerable
evidence that many migrants come for a shorter period (but nevertheless
make demands on services); and that others stay for longer than
they had originally intended.
75. London Councils argued that the exclusion from
population estimates of migrants who enter Local Authority areas
and use public services, but who did not settle for a year or
longer, was clearly penalising areas such as London which had
high levels of migration.
The definition of a resident from overseas for population
purposes, currently defined as a migrant intending to reside in
the UK for at least a year, has become increasingly important
over the last few years due to increasing numbers of short-term
migrants in the UK. This is a particular issue for London, as
demonstrated by recent experimental statistics published by the
ONS which suggest that 40% of all short-term migrants live in
London. Therefore, the current definition of a resident fails
to meet the need for population statistics for funding purposes
because they exclude a significant proportion of people who are
living in the capital. This means that Local Authorities that
experience influxes of short-term migrants do not receive funding
for people who are using their services. Thus, there is an urgent
need for estimates of short-term migration at the Local Authority
level, or for them to be included in existing population statistics.
76. The Sub-Committee received written evidence from
many Local Authorities across the country expressing similar concerns
about the impact of increased internal migration on resource allocation.
They also explained the need for both long-term and short-term
population estimates in order to plan service delivery.
77. One of the recommendations put forward by the
Inter-departmental Task Force on Migration Statistics was to produce
estimates of the number of short-term migrants.
In January 2007, the ONS published a report on the feasibility
of estimating short-term migration,
followed by feedback
in April and experimental estimates for England and Wales in October.
78. The ONS research report on short-term international
migration published in October provides estimates of short-term
migration at the national level for England and Wales. A regional
split of London/non-London is also provided. Estimates of short-term
migration are based on the United Nations definition of a short-term
migrant: someone who moves to a country other than that of his
or her usual residence for a period of at least 3 months but less
than a year (12 months) for study or employment purposes.
79. Taking the ONS's recent work on Short-Term Migrants
as an example, there are estimated to have been only 43,000 Short-Term
Migrants in England and Wales in the year up to June 2005, with
just 16,000 of these in Greater London. These estimates are based
on the International Passenger Survey, and appear to many users
to be implausibly low when contrasted with administrative data
such as National Insurance Numbers, which in 2005-6 recorded 235,640
new National Insurance Number registrations in Greater London
alone. Many of the latter no doubt returned to their countries
of origin within 12 months, but having the National Insurance
Number counts available provides a valuable additional insight.
80. The recently published ONS experimental short-term
migration estimates, although a welcome development towards estimating
the true population, do not reflect the scale of migration in
London that is evident from other administrative sources of data
e.g. National Insurance registrations. Further work would be needed
to improve these estimates and the sample sizes of international
migrants entering the country need to be improved considerably
to place greater confidence on the data.
81. ONS recognised the need to produce sub-national
short-term migration estimates and was currently investigating
the feasibility of producing estimates of the number of short-term
migrants at local level. The Sub-Committee received evidence stressing
the importance of ONS being allocated sufficient resources to
produce robust local estimates of short-term migration.
82. The Statistics Commission stated that the accuracy
of population estimates varies geographically across the country.
Urban areas for example, characterised by large student and migrant
populations, multi-occupancy households and 'part-time' residents,
are subject to greater uncertainty in their population estimates
than rural areas. The Statistics Commission suggested that ONS
carry out a series of Local Authority case studies to investigate
and create a good practice guide on different data sources available.
Mr Dugmore argued that the accuracy of different administrative
registers should be compared with the 2011 Census in view of the
possibility of using administrative and population registers in
counting the population in the future.
mid-year population estimates, based on the 'usually resident'
definition of population, do not include short-term migrants.
Such estimates do not fully meet the needs of Local Authorities
and commercial users who are also interested in, for example,
short-term migrants as well as day-time and week-day populations.
We recommend that the Statistics Authority investigate the feasibility
of producing population estimates based on different measures
of population, such as estimates which include short-term migrants
and estimates which include the day-time population of Local Authorities.
84. We are seriously
concerned about the reliability and validity of ONS estimates
of short-term international migrants. Evidence from administrative
data sources such as the National Insurance Number register suggests
the ONS estimates do not reflect the scale of short-term migration
in England and Wales. We recommend that the Statistics Authority
examine the feasibility of producing estimates of short-term migration
at sub-national level, using the successor to the International
Passenger Survey that we recommended earlier and a greater range
of administrative data.
85. We further
recommend that the Statistics Authority continue the ONS's work
with Local Authorities and carries out a series of case studies
to identify alternative administrative data sources. These include
the National Insurance Number register, GP lists, other health
service lists, council tax records, and various registers on children
and school children. Although we recognise that different areas
have different problems associated with counting the population
and administrative registers, we recommend that the Statistics
Authority produce a best practice guide.