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Population Estimates for England and Wales

BSPS Seminar

Population Estimates Unit&

Improving Migration and Population Statistics (IMPS)

www.statistics.gov.uk/popestwww.statistics.gov.uk/imps

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Aims of the Seminar

• To gain a better understanding of the population estimates methodology

• To be aware of the sources used• To allow delegates to contribute ideas and expertise

on two important issues relating to population estimates: ‘Quality Assurance’ and ‘Defining Usual Residence’.

• To provide an overview of the work being undertaken as part of the Improving Migration and Population Statistics (IMPS) project.

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The ONS population estimates:– National level for England, Wales – Below national level, regions and local areas:

including local authorities (LAs) and primary care organisations (PCOs)

– By age and sex – By marital status– For total population and for household population– Annual one year in arrears (mid-2005 due to be

published 24 August 2006)

Population Estimates - Overview

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The ONS population estimates are of the resident population and are as at 30 June

The national resident population is:– all those usually resident regardless of nationality– members of HM and US armed forces stationed in

England and Wales. HM forces stationed overseas are not included.

Currently looking at new definitions e.g. daytime population, weekday population.

Population Estimates - Definitions

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The key uses of the population estimates:– Base for the population projections that are used for local

government resource allocation– Also used as denominators in resource allocation– Planning by central and local government e.g. services for

the elderly– Monitoring - used mainly as denominators in rates and ratios

e.g. fertility and mortality rates– Grossing up survey results e.g. Labour Force Survey– Research by academics and others– Commercial Usage

Population Estimates – Uses

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• Cohort component method:

Pt = Pt-1 + Bt - Dt + It

Population = Base (aged on) + Births - Deaths + net Migration

Most recent Census as the base (adjusted), Then update annually by adding births, subtracting deaths

and allowing for net migration National and subnational, “top down”.

Population Estimates – Methods 1

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Population Estimates - Methods 2 Static Populations

• These are sub-populations that don’t ‘age-on’ and are not covered by our estimates of Internal and/or international migration– Armed Forces, Prisoners, School Boarders

Method• Remove these sub-populations (previous year)• Age on rest of population• Add in new sub-populations (current year)

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Census as a base

• Only complete enumeration of the population (especially at a person level)

• Uses a similar definition of usual residence to the population estimates

• Once a decade the population estimates are rebased using the most recent Census

• Many distributions at local level are also based on Census data

• Very accurate source

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Births and DeathsSources

• Birth Registrations– Provided by Vital Statistics Outputs Branch

(VSOB) in ONS

• Death registrations – Also provided by VSOB– Adjusted from age at death to give age as at mid-

year (by VSOB)

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BirthsMethodology

• Births added on to population at age zero.

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BirthsChallenges

• Assume births abroad = births to non E&W residents– these births are allocated in proportion to the

number of females of ‘childbearing age’ (15-44)• Births to non-resident mothers is a big issue.• Allocation of 0 year old migration.• Unlike deaths (more later) age at birth not an issue -

not many people are born already aged 30!

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DeathsMethodology

• Subtract deaths from base

BUT

• January to June data are not final

• So adjusted for late registrations by:

– ‘adding on’ adjustments for previous year

– assumes adjustments are small

– assumes level of adjustments similar across years

– avoids need for annual revision

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ChallengesDeaths

• Very accurate source -– but not perfect

• Late Registrations (some now included)• Incorrect date of birth recorded• Deaths abroad vs. Deaths of non residents

– Deaths ‘Elsewhere’ allocated in proportion to other deaths

• Residence issues

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Internal MigrationDefinitions

Definition• A person who changes their place of usual residence

within the United Kingdom

• Internal migration is measured by looking at GP re-registrations

• An Internal migrant is someone who – notifies their current GP of a change of address or– registers with a new GP in a different area from their

previous GP

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Internal MigrationSources 1

• National Health Service Central Register (NHSCR)– Moves between former HAs

• General practitioners’ (GPs) patient registers– Lower geography but only annual download

• Points to note– Reliant on registration with doctor– Possibly differing propensity to register– Time period is end July to end July

(one month delay in registering allowed)– Armed forces and (currently) prisoners excluded

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Internal MigrationSources 2

Combining the two sources:

• Estimate moves between former health authorities for those aged one and over, from both sources

• Derive scaling factors to apply to patient register data

• Derive estimates for under-1s from estimates for one year-olds

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International MigrationDefinitions

• International MigrationCivilian migration between the UK and the rest of the world

• International MigrantA person who changes his or her country of usual residence for a period of at least a year

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International Migration – Overview 1

Total International Migration (TIM) estimates

= International Passenger Survey migration data

– Migrant Switcher adjustment

+ Visitor Switcher adjustment

+ Asylum Seeker adjustment

+ Irish flows

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Migrant Switchers

IPS Migrants

Visitor Switchers

Asylum Seeker Adjustment

Irish Flows

TotalInternationalMigration

International Migration - Overview 2

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Irish (Eire) Flows

• The International Passenger Survey (IPS) does not cover people crossing the Northern Ireland/ Republic of Ireland border

• Therefore, an estimate of migrants to and from the Republic of Ireland needs to be made, using another data source

• To avoid double-counting, any of these migrants captured by the IPS are removed from the IPS component

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Irish (Eire) FlowsSources

• Data supplied by Migration Statistics Unit:

– by country & gender

– provided by CSO(Ireland)

– based on responses to the Irish Quarterly National Household Survey (April)

• These estimates cover:

– In migrants to Eire from E&W in the last 12 months

– Out migrants to E&W who were living in Eire 12 months ago

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Irish (Eire) Flows Methodology 1

• Split country totals to HA level

- Using 2001 E&W Census Distributions

Inflows: previous address 1 year ago in Eire

Outflows: country of birth: Eire

• Split HA totals to LA level

Inflows: previous address 1 year ago in Eire

(2001 E&W Census)Outflows: previous year resident population

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Irish (Eire) Flows Methodology 2

• Apply age-sex distribution- Using data from the E&W and Irish Censuses- National age-sex distribution used

Inflows: 2001 E&W Census Outflows: 2002 Irish Census

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Asylum Seeker Adjustment Definition

• Inflows are those coming into the UK claiming asylum:– who are granted asylum or– whose case will take 12 months or more to process

• Outflows include people ‘removed’; people who have withdrawn their application and state their intention to leave; and an estimate of the proportion of ‘failed asylum seekers’ who leave

• The ‘asylum seeker adjustment’ only includes asylum seekers missed by the IPS

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Asylum SeekerSources

• Migration Statistics Unit (from Home Office data):– AS inflow and outflow data for Principal & Dependent

applicants:• UK by sex & quinary age groups• GORs

• Home Office:– NASS (National Asylum Support Service)– Provides figures on subsistence and accommodation

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Asylum SeekerMethodology

Using the NASS data

• For each LA calculate the number of AS in receipt of an allowance (either accommodation and subsistence or subsistence only)

• Calculate the distribution within each GOR.

• Also calculate the distribution for subsistence only recipients.

• Assume 70% of AS applicants (and their dependents) in receipt of an allowance and the remaining 30% have a similar distribution to those receiving subsistence only

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Asylum SeekersChallenges

• Definition difference between Population Estimates and National Population Projections.– Use successful Asylum Seekers

• Failed Asylum Seekers: Simply not sure where they go – is proportion correct?

• Distributions: – Use of National age-sex distribution at LA level– Expanding quinary age groups using equal

spread/ 85 cut-off

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International Passenger Survey (IPS)

• Continuous voluntary sample survey

• Conducted by ONS since 1964

• Tourism, balance of payments and migration

• Principle air, sea & Channel Tunnel routes

• Approximately 0.2% of all travellers sampled -

immigration filter shifts increase sample size

• Based on intentions for ‘Length of Stay’

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Migrant data

Visitor data

IPS - ‘Length of Stay’ Question

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International Migration (IPS)Sources

• Data provided by Migration Statistics Unit:– by age & sex– by HAs

• High Weights data

High Weights:

Where 1 IPS contact is grossed to an excess of 1000.

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International Migration Methodology 1

• Calculate GOR Totals

- Aggregate IPS data (incl. high weights) to GOR to produce GOR totals

• Calculate an HA distribution (excl. high weights)

- Subtract high weights from IPS HA totals to produce ‘HA distribution’ for each GOR

• Apply ‘HA distribution’ to GOR total to produce new HA totals

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International Migration Methodology 2

• The HA totals are then smoothed over 3 years:

3yr HA total x GOR total (current year)

3yr GOR total• Split by LA within HA:

– Inflows: using Census distribution: usual address 1 year ago (all immigrants)

– Outflows: using previous year’s population distribution

• Apply National age-sex distribution (IPS)

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International MigrationChallenges

• Overlap with Armed Forces– Particular areas difficult to estimate.Outflows for

these areas may result in an underestimation.• First Onward Moves:

– Links between Internal and International Migration. May be missing vital data.

• Sample Variation• Intentions vs. Actuality

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Visitor and Migrant Switchers Definitions

• Migrant Switchers (Subtracted):– Persons who state the intention (in the IPS) to stay

in the destination country for more than a year but who actually leave sooner.

• Visitor Switchers (Added):– Persons who enter (or leave) the UK as visitors,

but subsequently extend their visit to 12 months or longer.

– Includes both EEA and non-EEA people

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School Boarders Sources

• England - DfES (Department for Education and Skills, Pupil Statistics Unit)

• Wales - WAG (Welsh Assembly Government, Statistical Directorate)

• Collected on annual returns from schools.• Includes public and state schools.

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School BoardersMethodology

• Compare previous year figures with current year to derive annual change figure.

• Add annual change to population base.• Schools allocated to LA based on postcode.• Information on boarders collected at SYOA, 7 to 18.

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School BoardersChallenges

• Data Quality– Data on 81,500 boarders in 860 schools received– Final Total 82,200 boarders from 920 schools– Missing Schools (forms not returned)– Schools incorrectly record day-pupils as boarders

• Is Definition of “boarder” suitable?• In recent times more schools have required local GP

registration - hence boarders may be captured through standard internal migration.

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PrisonsSources

• Home Office

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PrisonsMethodology

• Compare previous year figures with current year to derive annual change figure.

• Add annual change to population base.• Prisons allocated to LA based on postcode.• Information on prisoners collected at SYOA, 14 to

90+

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Prisons Challenges

• Quality of raw data– Prisons codes can be incorrect in source

• Combining of Prison medical service into NHS.

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Home Armed Forces (HAF)Methodology 1

• Mid-year population estimates include all people usually resident in England & Wales but NOT HM Forces (or their dependents) stationed overseas

• Data on HM Forces (incl. Gurkhas) received from Defence Analytical Services Agency (DASA)

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Home Armed ForcesMethodology 2

Each year• Remove previous year HAF resident in E&W• Add back in all previous year UKAF from E&W• Add previous year E&W service families overseas

Age on, then

• Remove current year UKAF from E&W • Add in HAF resident in E&W• Remove E&W service families overseas

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Home Armed Forces Methodology 3: UKAF from E&W

• Receive UKAF by age (16-59) & sex• Apply Census ratio to estimate those from England,

and from Wales

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Home Armed Forces Methodology 4:

HAF resident in E&W 1

• Receive HAF by sex by base LA – take average of Oct, Jan, Apr & July figures

• Re-distribute ‘Whitehall Warriors’ (These are armed forces personnel based in London doing ‘desk jobs’)– Remove a percentage (based on 1998 data) from

Westminister – Re-distribute across London using Census data

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Home Armed Forces Methodology 5:

HAF resident in E&W 2• Add in Gurkhas

– Receive Gurkhas by unit (all male)– Assign to base LA

• Use base-to-residence matrix from the Census assign to LA of residence (by sex)– Base county to resident LA matrix– For each county we only include LAs with more than

30 males or 10 females resident except where there is a small base

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Home Armed Forces Methodology 6:

HAF resident in E&W 3

• Apply age distribution by sex by LA from the Census• Constrain sub-national age-sex totals to national age-

sex totals provided by DASA

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Home Armed ForcesMethodology 7:

Service Children Overseas 1

Receive UKAF married men overseas by force• Apply scaling factors (based on 1998 data) by force

to estimate children overseas• Apply Census ratio to estimate those from England,

and from Wales• Assume equal number of male and female children

• Apply age distribution

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Home Armed ForcesMethodology 8:

Service Children Overseas 2

Age Distribution• Receive estimate of number of children in families

overseas receiving child benefit by age • Apply ‘boarding school factors’ (based on Census) to

remove those still at school in E&W (ages 11-14)

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Home Armed ForcesMethodology 9:

Service Wives Overseas

Receive UKAF married men overseas by force• Apply proportions (based on 1998 data) by force to

estimate wives overseas• Apply Census ratio to estimate those from England,

and from Wales• Assume wives have same age distribution as

husbands and apply age distribution for UKAF married men overseas.

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Home Armed ForcesSources 1

• DASA (Defence Analytical Services Agency)– UKAF by age (16-55+) and sex– HAF by age and sex and base LA– Gurkhas by unit– UKAF married men overseas by age and sex

• Her Majesty’s Revenue and Customs (HMRC)– Children in families overseas receiving child

benefit by age (based on 5% sample)

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Home Armed ForcesSources 2

• Census Distributions– UKAF from England, from Wales– Distribution of ‘Whitehall Warriors’– Percentage of UKAF children (aged 11-14) at

boarding school– Base-to-residence matrix– HAF by age and sex and LA

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Home Armed ForcesChallenges 1

• New data are now available on base LA age distributions – how do we use these data?

• Is the adjustment for ‘Whitehall Warriors’ required?• No residence based data currently available from

DASA – base-to-residence matrix may not reflect changes in living patterns over the decade

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Home Armed ForcesChallenges 2

• Use of base-to-residence matrix– County to LA or LA to LA

• Use of 1998 scaling factors/ proportions in service families abroad

• Assumption that wives have the same age distribution as their husbands

• Currently, UKAF from E&W and Service families overseas components only included at national level

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Foreign Armed ForcesMethodology

• Compare previous year figures with current year to derive annual change.

• Data include forces AND dependants.• Specific adjustment made as most people travelled

on military flights that are excluded from the IPS• IPS data excludes military personnel ‘on business’• Age and sex breakdown is based on Census.• Location information is based on postcode/ address.

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Foreign Armed ForcesSources

• Single point of contact is the United States Air Force, they collate from – United States Air Force 20,600– United States Navy 1,000– United States Army 700

• Census for distributions.

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Foreign Armed ForcesChallenges

• Data quality - sometimes invalid or missing postcode• No gender or age breakdown

– so Census age distribution gets progressively out of date

– If new LA, with previously no personnel, then what distribution should be applied?

• Dependent on goodwill of USAF - data supply issues and timeliness

• Security considerations

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Improving Migration & Population Statistics (IMPS)

• Briony Eckstein & Kanak Ghosh

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• Background to the Project

• Overview of the Project’s Objectives

• Overview of the Areas of Research

• More Detail:

– Local Authority Case Studies

– International Migration

– Internal Migration

– Administrative Data Sources

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Background – 2001 Mid-Year Estimates53,225,000

52,084,000

Rolled forwardfrom 1991

Based on2001 census

Original inter-censaldiscrepancy of 1.1 million

51.5m

53.5m

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Background – 2001 Mid-Year Estimates

Rolled forwardfrom 1991

Based on2001 census

Revised 1991post-censusadjustment

Internationalmigrationrevisions

2001 post-censusadjustments

- 351,000

- 305,000

+ 275,000

Remaining unexplaineddifference of 209,000

51.5m

53.5m

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CENSUS BASE

BIRTHS

DEATHS

INTERNALMIGRATION

INTERNATIONALMIGRATION

DIFFICULT /MOBILE GROUPS

NEW BASE

Did the 2001 census under- or over-estimate the population?

Did the 2001 census incorrectly apportion the One Number Census adjustments across local authorities within census Estimation Areas?

Are there births that do not get registered?Are there births registered where the baby should not be counted in the population?

Are there deaths that are not registered?Are there deaths which are registered in the wrong LA?

Are there people who move but do not register in the new area?Are there adults who never register, so remain counted where they were in full time

education?Are there people who move but the move is incorrectly counted because they

register in the new area but were not registered in the old area?

Are asylum seekers coming in correctly allocated to LAs?Are asylum seekers who leave correctly subtracted from LAs?How are asylum seeker centres accounted for?Are visitor switchers correctly allocated to LAs?Are other international migrants coming into the UK correctly allocated to LAs?Are other international migrants leaving the UK correctly subtracted from LAs?Are flows to and from Ireland correctly apportioned to LAs?

Armed Forces School Boarders PrisonersStudents

Are sex ratios plausible?Are age / sex percentages plausible?

Background – Possible Weaknesses

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• To improve the quality and reliability of migration and population statistics

• To ensure that the gap between the rolled forward mid-year estimates and the 2011 census results is not as large as was the case in 2001

• To ensure that ONS more fully understands the causes of/reasons for any gap that does occur in 2011

Overview – IMPS Key Objectives

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Overview – IMPS Work Streams• Population Base

• what population bases do users need?

• Alternative Data Sources• nationally held data• locally held data

• International Migration

• Internal Migration

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More detail – IMPS Work Streams

• Local Authority (LA) Case Studies• International Migration• Internal Migration• Administrative Data Sources

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Local Authority (LA) Case Studies

Investigate whether there are any locally held data sources which could be used to produce or quality assure the population statistics

• The selection of case study areas

• identify risk factors

• group LAs into clusters

• principal component analysis to identify clusters of interest

• LA nearest to centroid of each cluster selected

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LA Case Studies – Risk Factors

• Gross international migration

• Gross internal migration

• Armed forces

• Non-white population

• Full-time students aged 18-74

• Prisoners

• Men aged 20-39

• Population density

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LA Case Studies – Selected Clusters & LAs

Cluster 1 • high population density, migration

rates and proportion of young males• above national average proportions

of students and non-white population

Cluster 2• high proportion of non-white

population• above national average population

density, migration rates and proportions of students and young males

Cluster 8• above national average proportions

of non-white population, students and young males

Cluster 11• high proportion of students

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International Migration – Work StreamsNational Statistics Quality Review research

• International Passenger Survey (IPS) - migration questions and sampling

• methods used to integrate sources currently used to estimate international migration

• methods used for distributing IPS flows geographically within the UK

• potential use of existing alternative data sources to estimate international migration

Other international migration research

• short-term international migration

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International Migration

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

Distribution of inflows within the UK, 2001

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International Migration

Distribution of inflows to LAs within GORs

Proportion of all Immigrants to LAs in North East

0.00

0.10

0.20

0.30

0.40

0.50

0.60

LAD

Pro

po

rtio

n o

f A

ll I

mm

igra

nts

IPS

CENSUS

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Internal Migration

Research areas

• alternative data sources• benefits data for children and ‘older persons’• school census data for children• student data

• the under-recording of young male migration

• is the migration of other groups under-recorded?• ethnic minorities• non-English speakers

• the introduction of walk-in centres

• the closure of GP’s lists

• the assumptions for armed forces and their dependants

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Administrative Data Sources

Research the potential use of

• National governmental sources• schools’ census• national insurance• child benefit• ‘older persons’• electoral roll

• Local governmental sources• council tax• housing needs surveys

• Commercial sources• utility companies• commercial demographic databases (eg. ACORN)

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• Background to the Project

• Overview of the Project’s Objectives

• Overview of the Areas of Research

• More Detail:

– Local Authority Case Studies

– International Migration

– Internal Migration

– Administrative Data Sources

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Contact DetailsWebsite:

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

E-mail:

imps@ons.gov.uk

Telephone:

Briony (01329) 813672Kanak (01329) 813843