Combining migration data from multiple
sources: Applications to internal
movements in England, 1999-2007
James Raymer
with Peter W.F. Smith and Corrado Giulietti
Southampton Statistical Sciences Research Insitute (S3RI)
Centre for Spatial Analysis and Policy, University of Leeds, 19 February 2009
1
ESRC project on Combining Migration
Data in England and Wales
• Develop a methodology for combining migration
data and for producing ‘more detailed’ flows over
time
• Applications include flows by ethnicity, economic
activity and education at regional, county and area
group levels
Background
• Internal migration data in England are limited due
to differences in sources, availability, quality and
measurement, e.g.,
– National Health Service Central Register
– Census
– Labour Force Survey
Significance
• The combination of multiple data sources increases
the capacity to study migration and population
change for specific groups by producing
– harmonised data sets
– time series
• Estimates can be used for subnational projections,
planning or policies
Outline
• A general log-linear model for combining data
• Ethnic migration at regional level, 1991-2007
– Combining census and health registration data
– Results
• Economic activity migration at county level, 19992007
– Combining census, survey and health registration data
– Results
• Conclusions and future work
A general log-linear model for combining
migration data
• We are interested in estimating five-way migration
flow tables over time
• The five dimensions are origin, destination, age,
sex and some other ‘more detailed’ variable
• Migration flow tables are composed of various
hierarchical structures, not all of which are
necessary for accurate prediction
• If certain (important) structures are unavailable,
they can be ‘borrowed’ from auxiliary data sources
Log-linear models for origin, destination
and age migration flow tables
• Saturated model


ODA
OA
DA
ODA
log ijx
   Oi  Dj  xA  OD






ij
ix
jx
ijx
• Unsaturated model


ODA
log ijx
   Oi  Dj  xA  OD
ij
• Unsaturated-with-offset model


ODA
ODA
log ijx
   Oi  Dj  OD

log(
m
ij
ijx )
Ethnic migration
• Categorical variables
– 9 origins (O) and
destinations (D)
– 16 age groups (A)
– 2 sexes (S)
– 4 ethnic groups (E)
• 1991-2007 National
Health Service (NHS)
register*
– OD, OAS and DAS
tables each year
• 1991 and 2001
censuses
– ODAS and ODSE
* Males undercounted
Reported proportions of NHS interregional
migration in England by sex, 1991-2007
0.54
Proportion
0.52
0.50
Male
1991 and 2001 Census = 50.8 M and 49.2 F
Female
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
0.46
1991
0.48
120
100
80
60
40
Age Group
M 1991
F 1991
M 2007
F 2007
75+
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
5-9
0
10-14
20
0-4
Thousands
Age patterns of NHS interregional migration
in England by sex, 1991 and 2007
Adjustment ratios for NHS migration data
Year
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
15-19
1.315
1.287
1.300
1.294
1.322
1.334
1.339
1.348
1.344
1.343
1.388
1.393
1.399
1.400
1.390
1.399
1.400
Age Group
20-24
1.436
1.411
1.409
1.398
1.385
1.403
1.408
1.441
1.433
1.454
1.473
1.482
1.487
1.514
1.490
1.523
1.553
25-29
1.131
1.128
1.131
1.136
1.121
1.130
1.136
1.156
1.157
1.176
1.161
1.177
1.188
1.217
1.223
1.255
1.281
Males
1.123
1.117
1.120
1.116
1.117
1.122
1.119
1.125
1.122
1.127
1.131
1.130
1.132
1.137
1.138
1.145
1.148
Both
Sexes
1.059
1.056
1.058
1.056
1.056
1.058
1.057
1.059
1.058
1.060
1.062
1.062
1.063
1.065
1.066
1.069
1.070
Basic framework
• Data preparation
• Identification of key structures and theoretical
model
• Estimate the flows
• Analyse the results
Identifying the ethnic migration model:
Analysis of Census 2001 data structures
• ODAS table
– Key structures are OD, OA, DA and AS
• ODSE table
– Key structures are ODE, S
• Theoretical model (ODASE)
– ODE, OA, DA, AS
Model specification


NHSCR
Census

ODASE
OA
DA
AS
ODE
log ijxyz
 OD







log
m
ij
ix
jx
xy
ijz
Steps
• Construct time series of ODE tables using
geometric interpolation of counts from 1992
to 2000 and extrapolation to 2007
• Use iterative proportional fitting to estimate
flows, where the ODE tables are adjusted to
match simultaneously all of the counts
imposed by the NHSCR tables
• Adjust counts of males for three age groups

Thousands
Results: Estimated levels of South Asian,
Black and Chinese & Other interregional
migration in England, 1991-2007
80
% White
1991 = 94
2001 = 90
2007 = 85
70
60
50
40
30
20
10
0
1991
1993
1995
1997
South Asian
1999
Black
2001
2003
Chinese & Other
2005
2007
SE
70
EA
SE
7
6
EA
5
4
40
WM
3
SW
6
EA
SE
5
EA
2003
2001
1999
1997
1995
2007
2005
2003
2001
0
1999
0
1997
1
1995
1
1993
2
1991
2
1993
3
1991
WM
2007
SE
6
4
3
2005
2003
2001
1999
1997
7
2007
Thousands
7
Chinese & Other
8
2005
Black
8
1995
2007
2005
2003
2001
1999
1997
0
1995
0
1993
1
1991
10
1993
2
20
1991
30
4
NW
EM
EA
SW
South Asian
8
50
5
Destinations
NE
YH
WM
SE
LO
Thousands
Thousands
80
60
Thousands
Results:
Estimated
interregional
migration from
London
by ethnicity,
1991-2007
White
90
7
6
SW
30
EA
4
Black
Thousands
7
6
4
2007
2005
2003
2001
1999
2007
2005
2003
2001
1999
0
1997
0
1995
1
1993
1
2007
2
2005
2
2003
LO
3
LO
2001
1997
6
4
1999
1995
7
5
1997
Chinese & Other
8
5
1995
1993
2007
2005
2003
2001
1999
0
1997
0
1995
1
1993
10
1991
2
1991
3
20
3
LO
1991
Thousands
Thousands
40
8
South Asian
8
5
LO
50
1993
NW
EM
EA
SW
70
1991
Destinations
NE
YH
WM
SE
LO
80
60
Thousands
Results:
Estimated
interregional
migration from
South East by
ethnicity, 19912007
White
90
Results: Estimated age-specific migration of female South
Asians: 1991, 1999 and 2007
West Midlands to London
South East to London
300
900
800
700
600
500
400
300
200
100
0
250
200
150
100
50
0
0
5
10
15
20
25
30
35 40
45
50
55
60
65
70 75+
0
5
10
15
20
25
30
Age
1991
1999
2007
1991
200
150
100
50
0
5
10 15
20
25
30
35 40
45
50
55
60 65
70 75+
0
5
10 15
20
25
30
Age
1991
50
55
60
65
70 75+
1999
1999
60 65
70 75+
2007
London to South East
900
800
700
600
500
400
300
200
100
0
250
0
45
Age
London to West Midlands
300
35 40
35 40
45
50
55
Age
2007
1991
1999
2007
Economic activity migration
• Categorical variables
– 47 origins (O) and
destinations (D)
– 12 age groups, 15-74 (A)
– 2 sexes (S)
– 6 economic activity
groups (G): Self
employed, employee,
unemployed, retired,
other inactive and
students
• 1999-2007 NHS
Patient Registry Data
System*
– OD, OAS and DAS tables
each year
• 2001 census
– ODAS and ODSG
• 1999-2007 Labour
Force Survey
* Males undercounted
– AG and SG
160
140
120
100
80
60
40
Age Group
M 1999
F 1999
M 2007
F 2007
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
0
20-24
20
15-19
Thousands
Age patterns of PRDS inter-county migration
in England by sex, 1999 and 2007
Identifying the economic activity
migration model
• Theoretical model (ODASG)
– ODG, OA, DA, AS, AG, SG
• 1st step: Combine LFS and Census data
log

ODASG
mijxyz
 
AG
xz

SG
yz
 log

ODG
mijz

• 2nd step: Combine estimates from 1st step with
PRDS data



ODASG
OA
DA
AS
ODASG
log ijxyz
 OD







log
m
ij
ix
jx
xy
ijxyz

Thousands
Results: Overall levels of migration by
economic activity groups, 1999-2007
1,400
1,200
1,000
800
600
400
200
1999
2001
Employee
Student
2003
Inactive
Retired
2005
Self-Employed
2007
Unemployed
Results: Spatial patterns of employee and inactive
migration from Greater Manchester (top 10 flows),
1999
67% of all outflows
Employee
66% of all outflows
Inactive
20% of all outflows
15% of all outflows
10% of all outflows
5% of all outflows
2% of all outflows
20% of all outflows
15% of all outflows
10% of all outflows
5% of all outflows
2% of all outflows
Results: Spatial patterns of student migration from
Greater Manchester and Hampshire (top 10 flows),
1999
71% of all outflows
20% of all outflows
15% of all outflows
10% of all outflows
5% of all outflows
2% of all outflows
65% of all outflows
20% of all outflows
15% of all outflows
10% of all outflows
5% of all outflows
2% of all outflows
Results: Spatial patterns of retired migration from
Greater Manchester and Hampshire (top 10 flows),
1999
69% of all outflows
20% of all outflows
15% of all outflows
10% of all outflows
5% of all outflows
2% of all outflows
70% of all outflows
20% of all outflows
15% of all outflows
10% of all outflows
5% of all outflows
2% of all outflows
Results: Spatial patterns of retired migration from
Greater Manchester (top 5 flows), 1999-2007
600
2000
1500
400
1000
200
500
0
Lancashire
West Yorkshire
Merseyside
Devon
2007
2006
2005
2004
2003
2002
2001
2000
1999
0
Cheshire
Results: Age- and sex-specific migration of selected economic
activity groups from Greater Manchester (top flow), 1999
500
500
400
400
Employee to Cheshire
70-74
65-69
60-64
55-59
50-54
45-49
35-39
30-34
40-44
Male
Female
70-74
65-69
60-64
55-59
50-54
25-29
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
0
30-34
0
25-29
100
20-24
100
15-19
200
Female
Students to West Yorkshire
300
200
Female
45-49
Inactive to Lancashire
40-44
400
35-39
400
30-34
500
Male
25-29
Male
500
300
20-24
70-74
65-69
60-64
55-59
Female
20-24
Male
50-54
45-49
40-44
0
35-39
0
30-34
100
25-29
100
20-24
200
15-19
200
15-19
300
15-19
300
Retired to Lancashire
Conclusions
• Flexible model and framework for combining
migration data
– Level of detail
– Geography
– Sources of information
• Result is a synthetic data base that takes advantage
of several available data sources
• Estimates can be used for analysis, projections or
planning
Future work
• In the next six months
– Model ethnic migration flows at county level
– Extend approach to estimate flows by education
– Test model to predict flows between local authorities,
say, within a county or region
• In the next few years…
– Link this framework and resulting estimates with
subnational population modelling
– Extend this framework to analyse other transition data,
such as health, labour force and household change
Contact information
James Raymer
Southampton Statistical Sciences Research Institute (S3RI)
University of Southampton
Southampton SO17 1BJ
Email: [email protected]
See also Raymer J, Smith PWF and Giulietti C (2008) Combining
census and registration data to analyse ethnic migration patterns in
England from 1991 to 2007. University of Southampton Statistical
Sciences Institute Methodological Working Paper, M08/09. Available
at: http://eprints.soton.ac.uk/63739/01/s3ri-workingpaper-M08-09.pdf
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