Population Estimates

Jonathan Swan, ONS

Mid-year population estimates

The ONS mid-year population estimates:● At national level for England, Wales ● At subnational level, for regions and local

areas: including government office regions (GORs), strategic health authorities (SHAs) and local authorities (LAs)

● By single year of age (to 90+) and sex● Annually one year in arrears (mid-2005 were

published on 24 August 2006)● Estimate the population as at 30 June

Other Products

● Primary care organisation (PCO) estimates

● Marital status estimates

● Household population estimates (experimental)

● Quarterly population estimate (experimental)

● Small area population estimates (experimental)

● Ethnic population estimates (experimental)

● National population projections

● Subnational population projections

Currently looking at new population definitions, such as daytime population, weekday population.

Key uses of 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 - Methods

● 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”.

Methods (contd) – 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)

Cohort Component Method - National

Population = Base (aged on) + Births - Deaths + Net Internal migration (cross-border flows)+ Change in home armed forces in country

(UKAF, HAF, Overseas families)+ Change in foreign armed forces in country

(FAF, FAF dependents)+ Net International migration

(IPS, VS, AS, MS, Eire)

Cohort Component Method - Subnational

Population =

Base (aged on) + Births - Deaths

+ Net Internal migration

+ Change in school boarders

+ Change in prisoners

+ Change in home armed forces (HAF only)

+ Change in foreign armed forces (FAF, FAF dep)

+ Net International migration

(IPS, VS, AS, MS, Eire)

+ Boundary adjustment

+ Reconciliation Adjustment

Data Sources

Census - base and used for distributions Registration data - births, deaths NHSCR and GP Patient Registers - internal migration International Passenger Survey – international

migration Home Office - Asylum Seeker data DASA - Armed Forces US Army, Navy, and Air Force - Foreign Armed Forces DfES/ WAG –Boarding Schools Home Office - Prisoners

Internal Migration - Definitions

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

Internal Migration - 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

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

International Migration – Overview 2

Migrant Switchers

IPS Migrants

Visitor Switchers

Asylum Seeker Adjustment

Irish Flows

TotalInternationalMigration

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’

Proportion of inflows by UK countries/ English GORs

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

IPS Central Tendency in the North East

Proportion of all Immigrants to LAs in North East

0.00

0.10

0.20

0.30

0.40

0.50

0.60

LA

Pro

port

ion

of A

ll Im

mig

rant

s

IPS

CENSUS

Description of improved methodology (UK to GOR/Country)

● Calibration methodology developed for using LFS distributions to allocate IPS in-migrants at GOR/country level

Description of improved methodology (new intermediate geography)

● Group ‘positive’ central tendency LAs with surrounding LAs

● Not all LAs have positive central tendency or surround one that does

● Group remaining LAs to achieve a minimum number of contacts

● A ‘new migration geography’ created for all LAs in England & Wales outside London

IPS Intermediate Geography for London

Description of improved methodology (new intermediate geography - London)

● Country of birth used as basis for grouping● Cluster analysis used to group● Aim of grouping together areas which share

similar stocks of people born in different parts of the world

● Students treated separately● Distributed directly from GOR to LA using

Census data on usual address one year ago

Description of improved methodology (age-sex distribution at LA level)

● Currently a national IPS age-sex distribution is applied at LA level

● However, the age distributions for immigrants vary between LAs

Improved methodology : ● Cluster LAs together sharing similar age distributions

● The centroid (average) age distribution is applied to each LA in that cluster

● Six age distribution types identified separately for males and females

Six cluster centroid age distributions produced for female immigrants

New International Out Migrant Model

National: England and Wales

Wales North East North West

NEI1 NEI2

Newcastle-u-T Gateshead Wansbeck

Published IPS Wales/GOR

High weights adjustment

Published IPS national total

3 Year IPS average to

apportion GOR

Propensity to Migrate model to apportion NIGs

New Intermediate Geography (NIG)

Examples of New Intermediate Geography: North East and South East

Propensity to Migrate Model

• Uses linear regression to predict the number of migrants per head of population.

• Uses entry selection method to select from 111 socio, economic, and demographic variables.

• Used to apportion from New Intermediate Geography to local authority level.

• Significant improvement in model fit– R2 increases from 42% to 89.5%

Visitor and Migrant Switchers

● 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.

Task Force

● Placeholder

Future Work Programme

● Placeholder

Short Term Migrants – Slide under development

● Definition of Long-term● Definitions of Short Term● Consultation

Integrated Population Statistics System

● This is essentially a population register

● Linking various administrative and other data sources

● Removing the need for a Census, or something as extensive as the Census

● Dependent on initiatives such as ID cards, and removing some of the restrictions on sharing data across government

How to have an Impact (slide under development)

● Write to us: pop.info@ons.gsi.gov.uk

● Raise your issues through LGA to Discuss at the Central Local information Partnership (CLiP) Population Sub Group

● Attend the May Seminars

● Respond to Consultations

– Short-term Migrants

● Invite us to Groups – and contribute

● Publish Research (Population Trends, BSPS Conferences etc.)

For further information:

See:

Making a Population Estimate

Contact Population Estimates Unit :

tel: 01329 813318

email: Pop.info@ons.gov.uk

Visit the NS website:

www.statistics.gov.uk/popest and

www.statistics.gov.uk/imps