Measuring Migration

 

Issue date: 26 October 2007
Type: Statement

ONS recognises the importance of high-quality statistics on migration.

ONS produces high-quality estimates of long-term migrants – people arriving in or leaving the UK for a period of at least a year. In addition, ONS has for the first time recently produced experimental estimates of short-term migrants for England and Wales.

Central and local government need accurate and timely statistics to support the development and monitoring of new policies, to plan and resource delivery and to describe the social change that is taking place. There is general recognition that, while current estimates are the best possible with existing methods and data sources, improvements to the methods and sources are needed.

In a period of rapid change, international population migration (that is, individuals changing their country of usual residence) can have a profound effect on economic and social policy and service delivery, both nationally and locally.

Long-term international migration has been the largest component of population change in the UK in recent years. It has been larger than natural change – the difference between births and deaths – since 1999. New figures on short-term migration since 2003 provide further evidence of the recent increase in mobility.

Estimating international migration

International migration cannot be estimated from any single source of information. There is no official record kept of all people entering and leaving the country. In the absence of such information, ONS uses a range of sources.

The main source of information is the International Passenger Survey (IPS), an ONS survey that interviews people entering or leaving the country for all purposes, including tourism, business, visiting relations, studying and migration.

The survey asks people where they are heading for and how long they intend to stay. However, after entering a country, people might change their minds about their length of stay for a variety of reasons. Sometimes their length of stay depends on decisions made by others, such as employers and immigration control officials.

Each year, ONS publishes mid-year estimates of the usually resident population for the previous year. These include an estimate of the inward and outward flows of long-term migrants. The estimate for in-migration is calculated using:

  • the IPS, which samples about 250,000 people a year arriving and departing from 16 airports, 12 sea ports and using the Channel Tunnel.
  • the Labour Force Survey, which provides data on where recent in-migrants have settled.
  • Home Office administrative sources on asylum seekers.
  • the Irish Quarterly National Household Survey.

 For migrants who settle and register with a GP, the National Health Service Central Register together with information from patient registers about re-registrations with GPs are used to assist with estimates on where migrants move to after they enter the country.

For out-migration, the IPS is the only reliable source of data.

Improving the estimates

As mentioned above, changes in the pattern of international migration and the increasing importance of migration in population change have underlined the need for better estimates and for creating estimates of short-term migration.

Work has been underway since 2003 to identify improvements, and some have already been made. In October 2007 ONS published experimental estimates of short-term migration in the years to mid 2004 and mid 2005 for England and Wales as a whole, as well as for London and the remainder of the country combined.

In the longer term, the detailed count to be taken in the 2011 Census will provide information on international migrants, and developments such as e-Borders (planned to have full coverage by 2014) will assist in estimating migration flows.

In the meantime, it is essential that policymakers and others are supplied with the best possible estimates of migration.

In 2006 the Migration Task Force, an inter-departmental body led by ONS, was set up to consider how improvements might be made in the next few years. The task force made a number of recommendations. These included:

  • better surveying and monitoring of migrants entering and leaving the country.
  • better information about migrants living in the UK.
  • using a range of official data sources, such as tax and social security records, to improve information about migrants in the UK.
  • bringing together all the statistics collected across Government on migration and migrants in a single UK-wide report.

Improving migration statistics is a complex task and there is no quick fix. Implementing the task force’s recommendations will require extra resources and coordinated effort across Government. Work on all the areas identified could begin in the next two years, but the benefits will not be fully felt for several years.

Background documents

In September 2003, ONS issued the final report of the National Statistics Quality Review (NSQR) of International Migration Statistics 148.5 Kb Word document.

More information on the Migration Task Force is available. The full report can also be downloaded.

The methodology for measuring international migration is published in the appendices of the annual reference volume Series MN on international migration, Migrants entering or leaving the United Kingdom and England and Wales .

The subnational distribution of international migration estimates is described in Making a Population Estimate in England and Wales .

ONS has been working collaboratively with local authorities. Reports of four local authority Case Studies were published between February and June 2007. A final report will be published by the end of the year.

More information on some of the popular misconceptions about migration statistics is also available.