improved methods for population and migration estimates ons centre for demography may 2007

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 2002-5

• 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 level Jonathan Smith

• Improved geographical distribution of international out-migrants at:

– local authority level Fiona 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

TotalInternationalMigration(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

0% 10% 20% 30% 40% 50%

North East

North West

Yorks & Humb

East Midlands

West Midlands

East

London

South East

South West

Wales

Scotland

N. Ireland

IPS LFS CENSUS

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

0%

10%

20%

30%

40%

Wales North East North West Yorks &Humb

EastMidlands

WestMidlands

East London South East South West

Existing New

Difference between existing and new geographical distributions

-6%

-5%

-4%

-3%

-2%

-1%

0%

1%

2%

3%

4%

Wales North East North West Yorks &Humber

EastMidlands

WestMidlands

East London South East South West

Mid-2002 Mid-2003 Mid-2004 Mid-2005


distribution of

international in-migrants

at Local Authority level

Existing Method

England and Wales

Newcastle upon Tyne North Tyneside

Published IPSGOR/Wales

Local Authority

Intermediate Geography: HA/FHSAs

National Published IPS

3 Year IPS average used to

apportion GOR/Wales

Distributed to Local Authority using Census immigration

North East

Newcastle & N Tyneside

Geographic Level Data/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’

Percentage of all In migrants to LAs in North East

0%

10%

20%

30%

40%

50%

60%

70%

Local Authority

Pe

rce

nta

ge

of

No

rth

Ea

st I

n M

igra

nts

IPS

CENSUS

Ne

wca

stle

upo

n T

yne

Sun

derla

nd

Dur

ham

Lower Confidence Interval

Upper Confidence Interval





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

NewcastleIn-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


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-Students London Students

BrentStudents

LO2Non-Students

BrentNon-Students

BrentIn-Migration

BrentIn-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

Local Authority

Local Authority


Age Distribution

• Current Method – National Age Distribution

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

0-4

5-9

10-

14

15-1

9

20-2

4

25-2

9

30-3

4

35-3

9

40-4

4

45-4

9

50-5

4

55-5

9

60-6

4

65-6

9

70-7

4

75-7

9

80-8

4

85an

dove

r

Age Group

Per

cent

age

of A

ll In

tern

atio

nal I

n M

igra

nts

England & Wales

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

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

0-4

5-9

10-1

4

15-1

9

20-2

4

25-2

9

30-3

4

35-3

9

40-4

4

45-4

9

50-5

4

55-5

9

60-6

4

65-6

9

70-7

4

75-7

9

80-8

4

85+

Age Group

Per

cent

age

of A

ll In

tern

atio

nl I

n M

igra

nts

Group A

Group B


distribution of

international out-migrants

at Local Authority level

Existing Method

England and Wales

Published IPSGOR/Wales

Local Authorities

Intermediate Geography: HA/FHSAs

National Published IPS

3 Year IPS average used to apportion GOR

North East

Newcastle &

North Tyneside

Newcastle upon Tyne North Tyneside


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 Tyne North Tyneside 5 Other LAs

NEI1

North East

England and Wales


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– R2 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 10-14• 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

Actual length of stay

IPS Migrants

< 1 year

1 year +

< 1 year 1 year +

Intended length of stay


1 year +

< 1 year

IPS Migrants


< 1 year 1 year +

Subtract Migrant Switchers



IPS Migrants1 year +

< 1 year 1 year +

< 1 yearAdd Visitor Switchers


Subtract Migrant Switchers


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 SwitchersIdentifying Inflows of Migrant Switchers

Person leaves UK having stayed less than 12 months

Actual length of stay Actual length of stay

0-3 months 3-12 months

Migrant switcher question

When you last arrived

in the UK, how long did

you intend to stay for?

Intended length of stay Intended length of stay

less than 12 months 12 months +

MIGRANT SWITCHER

New IPS Questions – Visitor SwitchersIdentifying Inflows of Visitor Switchers

Person stays in UK for 12 months or more

Person leaves UK


less than 12 months

Intends to stay abroad

less than 3 months

(becomes UK resident)

12 months +

Intends to stay abroad

Person never leaves UK

3 months or more

VISITOR SWITCHER

Visitor switcher question

When you last arrived

in the UK, how long did

you intend to stay for?

FORMER


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

England & Wales

Existing adjustment

New adjustment

Impacts of new adjustment

(new adj - existing adj)

Migrant Switchers

Inflow -24,700 -15,100 9,600

Outflow -2,800 -12,000 -9,200

Net inflow -21,900 -3,100 18,800

Visitor Switchers

Inflow 49,400 45,500 -3,900

Outflow 19,000 12,500 -6,500

Net inflow 30,400 33,000 2,600

Overall

Net inflow 8,500 29,900 21,400

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 2007

http://www.statistics.gov.uk/statbase/product.asp?vlnk=14834

Improving Migration and Population Statistics

http://www.statistics.gov.uk/imps

Population Estimates

http://www.statistics.gov.uk/popest

Sub-National Population Projections




http://www.statistics.gov.uk/popest


Contact Details

Website: http://www.statistics.gov.uk/imps

E-mail: [email protected]




improved methods for population and migration estimates ons centre for demography may 2007

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