1. Improved Method for the Geographical Distribution of Out-Migrants
Fiona Aitchison and Jonathan Swan

2. Previous year’s resident population used to apportion HA/FHSAs
Former Method
Previous year’s resident population used to apportion HA/FHSAs

3. (Including new visitor switcher assumptions)
New Method
Geographic Level
Data/Methods
(Including new visitor switcher assumptions)

4. Factors available in the model
Armed Forces
Crime
Education
Employment
Ethnicity
Housing
Deprivation
Migration
Existing population
Socio-economic classification
Students
Tenure
Country of Birth

5. 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%

6. 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)

7. 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

8. Example of the model: 2006
In 2006 the variables below are used to form the model, in addition to a constant term.
Estimated in-migrants
Males aged 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%

9. 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

10. 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

11. International Migration Sex Ratios

12. 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

13. Sex Ratio – example grouping Out migrants, quintiles, variable membership

14. Sex ratios – Out Migrants London vs. Non London

15. Sex ratios - Conclusions
All the variants we examined for LA groupings 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.

16. International Out Migration Age Distribution

17. International Migration (IPS) age profiles

18. Allocation of British / Non British

19. Age Distribution of British out-migrants Grouping LAs (Males)

20. 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 …
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

21. Any Questions…