Improved Methods for Population and Migration Estimates ONS Centre for Demography May 2007

Improved population statistics methods in 2007 ONS is planning to make improvements in 2007 to the methods for distribution of the national population estimates to local areas. These principally concern how long term international migrant numbers are distributed locally

Improvements being implemented in Population Statistics in 2007 Improved distribution of international in-migrants Improved distribution of international out-migrants Improved assumption setting on proportion of people who change their intentions on length of stay (‘switchers’)

Improvements being implemented in Population Statistics in 2007 Improved distribution of international in-migrants: –Between England & Wales and between regions of England –From regions to local authority level (LAs) using 2 stage process via improved intermediate level geography –Improved age distribution of in-migrants Improved distribution of international out-migrants: –Between LAs using 2 stage process from regions to LAs via improved intermediate level geography –Improved age distribution of out-migrants Improved assumption setting on proportion of people who change their intentions on length of stay

ONS wider work programme on population statistics This work is part of ONS wider work programme on population statistics, which aims to –Improve population estimates between Censuses as well as the 2011 Census-based estimates, –minimise the risk of divergence between Censuses –providing a better understanding of the differences that remain between the Census and rolled forward estimates

Further improvements to population statistics Increased sample size of out-migrants in International Passenger Survey in January 2007 Reporting the recommendations of the Task Force on International Migration Review of port surveys Use of administrative data in population estimation Researching feasibility of estimating short term migration Reporting on two of four Local Authority Case Studies that started at the end of 2005

Timetable for improvements in 2007 Population estimates, based on the revised methods will be released in August –first release of figures for 2006 –revised estimates for the years Current sub-national population projections, based on the 2004 estimates, will be revised (September).

Timetable for further improvements Products from this work will be made available as soon as they are completed. No further revisions to existing population estimates will be made for at least two years.

Quality Assurance and Communication Methods were: subject to rigorous QA during development independent internal QA discussed at CLIP presented at conferences external QA panel May seminars explaining improvements and impacts

Improved Methods for Estimating International Migration Emma Wright, Jonathan Smith & Fiona Aitchison

Overview of Improvements Improved geographical distribution of international in-migrants at: –Wales/GOR level Emma Wright –local authority levelJonathan Smith Improved geographical distribution of international out-migrants at: –local authority levelFiona Aitchison Improved estimation of people whose intentions change with respect to length of stay Emma Wright

Improved geographical distribution of international in-migrants at country/GOR level

International Passenger Survey (IPS) Basis for estimates of long-term international migration Continuous voluntary sample survey conducted at majority of UK ports –Airports, Sea Ports & Channel Tunnel Migrants interviewed at the start of their stay – responses based on their intentions

Estimating Total International Migration Migrant Switchers IPS Migrants Visitor Switchers Asylum Seekers Irish Flows Total International Migration (TIM)

Labour Force Survey (LFS) Large sample survey of 60,000 households per quarter; most communal establishments not sampled International in-migrants identified as those resident overseas one year previously Geographical location of in-migrants based upon actual place of residence

Census Coverage of communal establishments as well as private households International in-migrants identified as those resident overseas one year previously Geographical location of in-migrants based upon actual place of residence

Proportion of UK immigrant inflows by UK countries/English regions, 2001

UK Country/English Region level: Comparison of IPS and LFS Higher percentage of international in- migrants allocated to London in IPS: –consistent over time –greatest for young adult age-groups Evidence from IPS and Longitudinal Study: –higher percentage of migrants intending to live in London state that they are likely to move on to a different area –migrants who move on quickly unlikely to be recorded in internal migration sources

UK Country/GOR level: Methodology IPS and LFS data used in combination : –Distribution of in-migrants in LFS used to allocate IPS in-migrants at GOR/country level Methodology developed: –worked at IPS-contact level and minimised changes to weightings –took account of London/non-London differences in distributions by age and sex –used three years’ LFS distributions for robustness

Change to country/regional distribution of in-migrants, mid-2004

Difference between existing and new geographical distributions

Improved geographical distribution of international in-migrants at Local Authority level

Existing Method Published IPS GOR/Wales Local Authority Intermediate Geography: HA/FHSAs NationalPublished IPS 3 Year IPS average used to apportion GOR/Wales Distributed to Local Authority using Census immigration North East Newcastle & N Tyneside Geographic LevelData/Methods

How are we improving distribution to LA? ‘Central tendency’ within regions Replace intermediate geography Harmonise methods estimates/projections Age distributions

Local area distribution of in-migrants: data sources considered Surveys –International Passenger Survey –Labour Force Survey (LFS) Census Administrative Sources –Worker Registration Scheme (WRS) –National Insurance Numbers –Patient Registers

IPS Data – Central Tendency Example of central tendency Newcastle Comparison between IPS and Census

Identifying Areas with a ‘Positive Central Tendency’

New Migration Geography In-migration (NMGi) Positive central tendency LAs Thirteen in total Grouped with neighbouring LAs Remaining LAs grouped - Sample size - Neighbouring LAs

New Method Overview – Outside London Newcastle In-Migration Controlled IPS Data at GOR Census data to LA Control to New Regional Total 3 Year IPS average to NMGi North East NE1 Newcastle Geographic LevelData/Methods Region NMGi Local Authority Local Authority

In-migration Within London IPS data London – unique as a city and region In-migration spread across London LFS data Household survey – not intention based Required to group LAs together Foreign students in LFS

Migration Geography in London

New Method Overview - London London Non-StudentsLondon Students Brent Students LO2 Non-Students Brent Non-Students Brent In-Migration Brent In-Migration Controlled IPS Data Census data to LA Combine Students & Non-Students Control to New Regional Total 3 Year LFS average to NMGi London NMGi Local Authority Geographic LevelData/Methods

Age Distribution Current Method – National Age Distribution

Improving Age Distribution Local Areas have different age profiles Students Workers Joining friends/family IPS data can’t be used directly – group LAs together Census – Similar in-migrant age distributions

Final Age Distribution Examples - Females

Improved geographical distribution of international out-migrants at Local Authority level

Existing Method Published IPS GOR/Wales Local Authorities Intermediate Geography: HA/FHSAs National Published IPS 3 Year IPS average used to apportion GOR Geographic LevelData/Methods Previous year’s resident population used to apportion HA/FHSAs

Limitations with Existing Method Method assumes that within the intermediate geography everyone is equally likely to migrate Intermediate geography has too few sample points in many areas – especially NE and North generally Intermediate geography is obsolete – health geography areas no longer used

Challenges to developing a new approach Very limited sources/information on international out-migrants Sample size is a big issue. –Sample size precludes direct estimation of migrants from IPS at LA level.

New Method Published IPS National GOR/Wales LAs Propensity to Migrate model used to apportion NMGo 3 Year IPS average used to apportion GOR Published IPS New Migration Geography for emigrants (NMGo) Newcastle upon TyneNorth Tyneside5 Other LAs NEI1 North East England and Wales Geographic LevelData/Methods

Examples of New Intermediate Geography: North East and South East Newcastle upon Tyne North Tyneside Portsmouth Brighton and Hove Reading

Propensity to Migrate Model Used to apportion from intermediate geography to local authority level. Uses model to predict the number of migrants per head of population. –Model uses linear regression –Forward Stepwise entry selection method Consists of a number of socio-economic and demographic factors. Model results in a significant improvement –The percentage of variance explained is increased –R 2 increases from around 40% to over 80%

Example of the Model: 2005 In 2005 the variables below are used to form the model, in addition to a constant term. Estimated in-migrants Females aged Persons in lower supervisory/technical occupations Persons in Black ethnic group Density: persons per hectare The model results are then scaled to the total of the New Migration Geography area (NMGo).

Evaluation of Model The Propensity to Migrate Model has been evaluated to ensure continuity over time A number of different models have been evaluated The variables included in the model will be re- assessed each year

Age distribution Existing Method: Applies national age distribution to all LAs New Method: Applies different age distributions to different types of LAs –LAs split into 2 groups London areas and large towns Other areas –Differences between British and Non-British citizen age profiles accounted for –Results constrained to national age distribution from IPS

Improved estimation of people whose intentions change with respect to their length of stay

Switchers: Background

Current Switcher Adjustments Migrant Switchers: 5 per cent of IPS migrant inflows 1 per cent of IPS migrant outflows Visitor Switchers: Fixed proportions of intended long stay visitors Different assumptions for EU and non-EU citizens

New IPS Questions New questions have been asked on IPS since 2004 Allow actual and intended length of stay to be compared Provide evidence to inform migrant switcher and visitor switcher adjustments

New IPS Questions – Migrant Switchers

New IPS Questions – Visitor Switchers

Analysis of new IPS questions: Migrant switchers 3.1 per cent of IPS in-migrants estimated to be migrant switchers, lower than the current adjustment of 5 per cent. 4.4 per cent of IPS out-migrants estimated to be migrant switchers, higher than the current adjustment of 1 per cent.

Analysis of new IPS questions: Visitor switchers Estimated proportion of intended long stay visitors that actually stay for a year or more: Inflows of EU citizens: 27% Inflows of other citizens:15% Outflows of EU citizens:31% Outflows of other citizens:10%

Overall impact of changes to visitor & migrant switcher estimates, mid-2005

Future Switcher Estimates Calculated for each half year period Calculation based on data from new IPS questions for the previous 3 years Estimates allocated sub-regionally based upon new geographical distributions of IPS in- and out-migrants

National Statistics Website Pages Improved Methods for Population Statistics Revisions in Improving Migration and Population Statistics Population Estimates Sub-National Population Projections

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