Improved Method for the
Geographical Distribution of
Out-Migrants
Fiona Aitchison and Jonathan Swan
Former Method
Geographic Level
National
Data/Methods
England and Wales
Published IPS
GOR/Wales
Intermediate
Geography:
HA/FHSAs
Local Authorities
North East
Newcastle &
North Tyneside
Newcastle upon Tyne
North Tyneside
3 Year IPS
average used to
apportion GOR
Previous year’s
resident population
used to apportion
HA/FHSAs
New Method
Geographic Level
Data/Methods
England and Wales
National
Published IPS
(Including new
visitor switcher
assumptions)
GOR/Wales
New Migration
Geography for
emigrants (NMGo)
LAs
Newcastle upon Tyne
North East
3 Year IPS
average used to
apportion GOR
NEI1
North Tyneside
5 Other LAs
Propensity to
Migrate model
used to apportion
NMGo
Factors available in the model
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Armed Forces
Crime
Education
Employment
Ethnicity
Housing
Deprivation
Migration
Existing population
Socio-economic classification
Students
Tenure
Country of Birth
Modelling methods considered
• Factor Analysis followed by Enter method Linear
Regression
– Created 4 or 5 components built from approximately 20
of the available 100+ variables.
– Model gave an R2 value of approximately 68%
– Disadvantage: Complex with hard to interpret results
• Forward-Stepwise Linear Regression
– Created model with 3 variables selected from the
available 100+
– Model gave an R2 value of approximately 78%
Modelling methods considered
• Forward-Stepwise Linear Regression with logged
variables
– Model gave an R2 value of approximately 75%
– Disadvantage: A number of variables could not have
logarithm taken
• Forward-Stepwise Linear Regression (direct count
of out-migrants)
Testing procedure
• Precision of model measured using the Average Square
Error (ASE) on a number of test sets of data
• Log model was found to be subject to bias towards
underestimation
Modelling Method
Indicative ASE
Factor Analysis
0.45
Stepwise Regression (Propensity)
0.26
Stepwise Regression (Logs)
0.28
• The stepwise regression model of propensity to migrate
was selected due to more plausible results
Example of the model: 2006
• In 2006 the variables below are used to form the
model, in addition to a constant term.
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Estimated in-migrants
Males aged 16-34 with limiting long-term illness
Persons in higher professional occupations
Females aged 40-44
Percentage of males in population
• Model results in a significant improvement
– The percentage of variance explained is increased
– R2 increases from around 40% to over 80%
– In 2006 R2 is 91%
Changes from Indicative Results
• Indicative results for revised 2002 to 2005
estimates were published in April 2007
• An additional variable, Country of Birth, was
included in the list of factors
• The intermediate geography was revised for the
West Midlands and Wales
• The models for these years have all changed
slightly in terms of the variables selected
Future Work
• It is not intended to change the modelling
methodology for at least the next two years
– The model will still be updated each year with new data
– Results from extra out-migrant filter shifts on IPS will
become available
• Further research in this area will be taken forward
as part of wider migration research
International Migration
Sex Ratios
Sex Ratio – Methodology Considered
• Group LAs into quartiles and/or quintiles
• In Migrants
– Grouped by sex ratio of Census one year ago resident
outside UK
• Out Migrants
– Grouped by sex ratio of resident LA population.
– Groups fixed by 2001 ratios and
– Variable groups by previous years population
considered.
• Research undertaken by Michelle Littlefield, ONSCD
Sex Ratio – example grouping
Out migrants, quintiles, variable membership
1.6
1.4
Quintile
1
2
3
4
5
1.2
1
0.8
0.6
2001
2002
2003
2004
2005
Sex ratios – Out Migrants
London vs. Non London
1.6
1.4
1.2
1
0.8
0.6
2001
2002
2003
Out of London
2004
London
2005
Sex ratios - Conclusions
• All the variants we examined for LA groupings
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produced broadly similar results.
Therefore, not able to determine stable groupings
of LAs for sex ratios.
London / non-London split produced results we
were not able to explain.
Therefore unable to produce method for sex-ratios
of international migrants.
So the national sex-ratio is used.
Subject of possible further research.
International Out Migration
Age Distribution
International Migration (IPS) age profiles
Proportion of total migrants in age group
0.35
non-British outmigrants
0.30
non British - inmigrants aged
on 2 years
0.25
0.20
0.15
0.10
0.05
0.00
0-4
5-9
10-14 15-19 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70+
Age
Allocation of British / Non British
70%
% non-British IPS contacts
60%
50%
40%
30%
20%
10%
0%
Mid-02
Mid-03
Mid-04
Mid-05
Mid-year
1
2
3
4
5
2-4
Age Distribution of British out-migrants
Grouping LAs (Males)
Out-migrants %
6
Cluster 1
Cluster 2
5
4
3
2
1
0
0
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Age
Summary of Age Distribution Approach
• For each sex separately
• Split into British non-British
– LAs grouped by quintiles – middle three grouped
– Quintiles on in-migrants as % of resident population
• Non British
– Use age individual LA distribution of in-migrants …
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but aged on two years
• British
– Split into two clusters
– Clusters based on resident population age distribution
– Use IPS quintile age distribution
– Split to SYOA based on Census in-migrant distribution
• Research undertaken by Karen Gask
Any Questions…