6. Notes and Definitions
Population Covered
The estimated population of an area includes all those usually resident there, whatever their nationality. Students are treated as being resident at their term-time
address. Members of UK and non-UK armed forces stationed in Scotland are included; UK forces stationed outside Scotland are excluded. Short-term international migrants, who stay for less than 12 months, are excluded.
Age
Population figures relate to 30 June of the year shown and ages relate to age last birthday.
Presentation of Results
Although the populations are tabulated in units, this does not imply accuracy to that
level. The data are presented in units for the convenience of users wishing to compile non-standard aggregations without encountering rounding problems.
Administrative Areas
The composition of the NHS Board areas in terms of Council areas is summarised in the table below. From 1 April 2006 responsibility for NHS Argyll & Clyde was split between NHS Greater Glasgow (now known as Greater Glasgow and Clyde) and NHS Highland. The tables presented in this report present information for the new NHS Board areas for all years.
Composition of NHS Board areas
NHS Board area |
Council area |
Ayrshire & Arran |
East Ayrshire, North Ayrshire, South Ayrshire |
Borders |
Scottish Borders |
Dumfries & Galloway |
Dumfries & Galloway |
Fife |
Fife |
Forth Valley |
Clackmannanshire, Falkirk (part), Stirling (part), Perth & Kinross (part) |
Grampian |
Aberdeen City, Aberdeenshire, Moray |
Greater Glasgow & Clyde 1 |
East Dunbartonshire, East Renfrewshire, Glasgow City, Inverclyde, North Lanarkshire (part), Renfrewshire, South Lanarkshire (part), Stirling (part), West Dunbartonshire |
Highland 1 |
Highland, Argyll & Bute |
Lanarkshire |
North Lanarkshire (part), South Lanarkshire (part), West Lothian (part),Falkirk (part) |
Lothian |
East Lothian, City of Edinburgh, Midlothian, West Lothian (part),Falkirk (part) |
Orkney |
Orkney Islands |
Shetland |
Shetland Islands |
Tayside |
Angus, Dundee City, Perth & Kinross (part) |
Western Isles |
Eilean Siar |
1 New NHS Board areas including parts of former Argyll & Clyde.
Note: In practice there are some other very small "slivers" where NHS Board and Council area boundaries cross.
Land Area
The land areas used to calculate the population density information presented in Table 10 were derived from digital boundaries used for the 2001 Census.
Sources of migration data
Migration is the most difficult component of population change to estimate, as there is no comprehensive system which registers migration in the UK, either moves to or from the rest of the world, or moves within the UK. Estimates of migration have therefore to be based on survey data and the best proxy data that exist.
Migration estimates are derived from three key sources of data. The National Health Service Central Register (NHSCR) is used to calculate moves between NHS Board areas within the UK, with migration at Council area and below estimated using anonymised data from the Community Health Index (CHI). The International Passenger Survey (IPS) provides information on moves into and out of Scotland information is used for migrants to and from the Republic of Ireland and asylum seekers. These three main sources are described in more detail in the remainder of this section.
Internal migration within the UK
The NHSCR system records the movements of patients between NHS Board areas in the UK. Each time a patient transfers to a new NHS doctor in a different NHS Board area, the NHSCR is notified and then the patient is considered to have made a migrant move. Counts of these re-registrations are used as a proxy indicator for moves within the UK.
The CHI holds records of people registered with an NHS doctor in Scotland. Unlike the NHSCR, the records provided to the General Register Office for Scotland (GROS) contain the postcode of the patient's address, which enables migration to be estimated for councils, and for smaller areas. The approach used for estimating council-level migration involves matching CHI patient records extracted from a database which reflects the ‘live’ CHI system on two occasions one year apart.
Currently, GROS migration data derived from the NHSCR is considered to be the most reliable data available at NHS Board level, so estimates from the CHI are controlled to ensure that they are consistent with the NHSCR data for moves across a NHS Board boundary by origin, destination, age and sex.
Due to an improvement in data sources, the accuracy of cross border migration data between Scotland and Northern Ireland will be improved from mid-2009. More information on the nature of the improvements will be available following the May 2010 meeting of the Population and Migration Statistics Committee (PAMS). The papers will be available from June 2010 on the GROS website: http://www.nrscotland.gov.uk/statistics-and-data/statistics/user-consultations-groups-and-seminars/the-population-and-migration-statistics-committee-scotland-pams
International migration
An international migrant is defined by the United Nations (UN) as someone who changes country of residence for 12 months or more. There is no single, all inclusive system in place to measure all movements of population into and out of the UK. Therefore, it is necessary to use a combination of data from different sources that have different characteristics and attributes in order to produce estimates of international migration. While offering the best data currently available, none of the data sources used is specifically designed to capture information solely on international migration.
Three sources of data are used to compile the national estimates of international migration into Scotland:
Given that the IPS collects information on intentions which may or may not be realised, an adjustment is made to the IPS data for visitor and migrant switchers (people who change their intentions and their migratory status). The Long-Term International Migration (LTIM) estimate (previously referred to as Total International Migration, TIM) is derived by combining these components.
The IPS provides an estimate of international migrants into the United Kingdom. The allocation of these migrants to Scotland is based on the LFS. The LFS provides more reliable data on the geographical distribution of immigrants than the destination provided in the IPS as it is based on where migrants actually live rather than on their initial intentions. The outflow of international migrants from Scotland is based directly on the IPS data. More information on the LTIM method can be found in the Office for National Statistics (ONS) website: http://www.ons.gov.uk/ons/publications/re-reference-tables.html?edition=tcm%3A77-228078
This is the third year in which the LTIM estimate for Scotland has been used for the mid-year estimates for Scotland. Previously, GROS used a similar method based on the IPS, but this did not use the LFS distribution or include estimates of migrant switchers. It did however use an adjustment for unmeasured migration. The results of the 2001 Census indicated that the previously published 2000 mid-year estimates had been overestimated as a result of cumulative errors in estimating migration. To ensure that migration estimates did not continue to be overestimated, an unmeasured migration adjustment was included. The LTIM methodology does not include this adjustment. Rather the assumption is that, since the census and estimates are calculated using different methodologies, differences inevitably arise.
An evaluation of the impact of changing method has been carried out. The conclusion was that the GROS method estimated a cumulative net migration gain around 9,700 higher than the TIM method between the census and the 2006 estimates. There are currently no plans to revise the previous mid-year estimates.
Distribution of International Migrants to Scotland
International migration flows to NHS Boards were allocated by using overseas inflows recorded on the NHSCR. However, NHSCR records hold limited data on international outflows from NHS Boards to overseas, as patients rarely de-register with their doctor when moving overseas. As a result international outflows were allocated using averaged proportions based on international inflows, outflows to the rest of the UK and the population size of each NHS Board.
Age and sex distributions of international in-migrants are obtained directly from the NHSCR. The age/sex distribution of moves for international out-migrants was based on the distribution of migrants to the rest of the UK, as recorded by the NHSCR.
The distribution of migrants to Council areas is based on records from the Community Health Index (CHI), which are made consistent with the NHSCR geographic and age / sex distributions. International in-migrants were allocated using records appearing on the CHI extract where the patient had arrived from overseas. Like the NHSCR, the CHI extract holds limited data on people leaving Scotland for overseas and so international out-migrants were allocated using a combination of in-migrants to Scotland from overseas and migrants leaving Scotland for the rest of the UK.
Work to improve the method used to allocate international out-migrants to NHS Board and Council areas is continuing and further improvements will be considered for future publications.
Additional Migration Data
The GROS website now includes a migration section which provides additional tables showing migration estimates associated with mid-year population estimates. This can be accessed through the following link: http://www.nrscotland.gov.uk/statistics-and-data/statistics/statistics-by-theme/migration
Research into improving Migration and Population Statistics
It is increasingly important to have high quality statistics on migration and the population, for policy development and for planning and providing public services. Achieving this aim is challenging in the context of increasingly complex lifestyles and changes in migration to and from the UK over the last decade.
It was in this context that the National Statistician set up the Inter-Departmental Task Force on Migration Statistics to make recommendations on timely improvements that could be made to estimates of migration and migrant populations in the United Kingdom, both nationally and at a local level. The report of the Inter-Departmental Task Force on Migration Statistics was published on 15
December 2006 by the ONS. GROS represented the devolved administrations on this task force, and is working with the ONS on the implementation of the recommendations through the Improvements to Migration and Population Statistics (IMPS) cross-government programme.
The IMPS workplan involves:
GROS is involved in a number of workstreams within this programme with the aim of incorporating the research into their outputs. More details can be found on the GROS website http://www.nrscotland.gov.uk/statistics-and-data/statistics/statistics-by-theme/migration/migration-statistics/migration-statistics-improvements
More detail on the IMPS programme is available from the following link on the ONS website http://www.statistics.gov.uk/about/data/methodology/specific/population/future/imps/updates/default.asp