Population Estimates for
England and Wales
BSPS Seminar
Population Estimates Unit
&
Improving Migration and Population Statistics (IMPS)
www.statistics.gov.uk/popest
www.statistics.gov.uk/imps
1
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.
2
Population Estimates - Overview

3
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 - Definitions



4
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 – Uses

5
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 – Methods 1
• Cohort component method:
Pt = Pt-1 + Bt - Dt + It
Population = Base (aged on) + Births - Deaths + net
Migration



6
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 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)
7
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
8
Births and Deaths
Sources
• 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 midyear (by VSOB)
9
Births
Methodology
• Births added on to population at age zero.
10
Births
Challenges
• 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!
11
Deaths
Methodology
• 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
12
Challenges
Deaths
• 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
13
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 reregistrations
• 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
14
Internal Migration
Sources 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
15
Internal Migration
Sources 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
16
International Migration
Definitions
• International Migration
Civilian migration between the UK and the rest of the
world
• International Migrant
A person who changes his or her country of usual
residence for a period of at least a year
17
International Migration –
Overview 1
Total International Migration (TIM) estimates
= International Passenger Survey migration data
18
–
Migrant Switcher adjustment
+
Visitor Switcher adjustment
+
Asylum Seeker adjustment
+
Irish flows
International Migration - Overview 2
Irish Flows
Asylum Seeker Adjustment
Visitor Switchers
IPS Migrants
Migrant Switchers
19
Total
International
Migration
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
20
Irish (Eire) Flows
Sources
• 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
21
Irish (Eire) Flows
Methodology 1
• Split country totals to HA level
- Using 2001 E&W Census Distributions
Inflows:
Outflows:
previous address 1 year ago in Eire
country of birth: Eire
• Split HA totals to LA level
Inflows:
Outflows:
22
previous address 1 year ago in Eire
(2001 E&W Census)
previous year resident population
Irish (Eire) Flows
Methodology 2
• Apply age-sex distribution
- Using data from the E&W and Irish Censuses
- National age-sex distribution used
Inflows:
Outflows:
23
2001 E&W Census
2002 Irish Census
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
24
Asylum Seeker
Sources
• 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
25
Asylum Seeker
Methodology
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
26
Asylum Seekers
Challenges
• 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
27
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’
28
IPS - ‘Length of Stay’ Question
Migrant data
Visitor data
29
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.
30
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
31
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)
32
International Migration
Challenges
• 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
33
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
34
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.
35
School Boarders
Methodology
• 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.
36
School Boarders
Challenges
• 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.
37
Prisons
Sources
• Home Office
38
Prisons
Methodology
• 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+
39
Prisons
Challenges
• Quality of raw data
– Prisons codes can be incorrect in source
• Combining of Prison medical service into NHS.
40
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)
41
Home Armed Forces
Methodology 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
42
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
43
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
44
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
45
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 agesex totals provided by DASA
46
Home Armed Forces
Methodology 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
47
Home Armed Forces
Methodology 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)
48
Home Armed Forces
Methodology 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.
49
Home Armed Forces
Sources 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)
50
Home Armed Forces
Sources 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
51
Home Armed Forces
Challenges 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
52
Home Armed Forces
Challenges 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
53
Foreign Armed Forces
Methodology
• 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.
54
Foreign Armed Forces
Sources
• 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.
55
Foreign Armed Forces
Challenges
• 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
56
Improving Migration & Population
Statistics (IMPS)
• Briony Eckstein & Kanak Ghosh
57
• 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
58
53.5m
Background – 2001 Mid-Year Estimates
53,225,000
Original inter-censal
discrepancy of 1.1 million
52,084,000
51.5m
Rolled forward
from 1991
59
Based on
2001 census
Background – 2001 Mid-Year Estimates
53.5m
- 351,000
- 305,000
Remaining unexplained
difference of 209,000
+ 275,000
51.5m
Rolled forward
from 1991
60
Revised 1991
post-census
adjustment
International
migration
revisions
2001 post-census
adjustments
Based on
2001 census
Background – Possible Weaknesses
CENSUS 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?
BIRTHS
Are there births that do not get registered?
Are there births registered where the baby should not be counted in the population?
DEATHS
Are there deaths that are not registered?
Are there deaths which are registered in the wrong LA?
INTERNAL
MIGRATION
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?
INTERNATIONAL Are visitor switchers correctly allocated to LAs?
MIGRATION
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?
DIFFICULT /
MOBILE GROUPS
NEW BASE
61
Armed Forces
School Boarders
Are sex ratios plausible?
Are age / sex percentages plausible?
Students
Prisoners
Overview – IMPS Key Objectives
• To improve the quality and reliability of migration and
population statistics
• To ensure that the gap between the rolled forward midyear 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
62
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
63
More detail – IMPS Work Streams
•
•
•
•
64
Local Authority (LA) Case Studies
International Migration
Internal Migration
Administrative Data Sources
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
65
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
66
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
67
International Migration – Work Streams
National 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
68
International Migration
Distribution of inflows within the UK, 2001
N. Ireland
Scotland
Wales
South Wes t
South Eas t
London
Eas t
Wes t Midlands
Eas t Midlands
Yorks & Humb
North Wes t
North Eas t
0%
10%
20%
IPS
69
30%
LFS
40%
CENSUS
50%
International Migration
Distribution of inflows to LAs within GORs
Proportion of all Immigrants to LAs in North East
Proportion of All Immigrants
0.60
IPS
0.50
CENSUS
0.40
0.30
0.20
0.10
0.00
LAD
70
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
71
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)
72
• 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
73
Contact Details
Website:
http://www.statistics.gov.uk/imps
E-mail:
imps@ons.gov.uk
Telephone:
Briony
Kanak
74
(01329) 813672
(01329) 813843