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Improved Method for the Geographical Distribution of Out-Migrants

Improved Method for the Geographical Distribution of Out-Migrants. Fiona Aitchison and Jonathan Swan. Former Method. Previous year’s resident population used to apportion HA/FHSAs. New Method. Geographic Level. Data/Methods. (Including new visitor switcher assumptions).

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Improved Method for the Geographical Distribution of Out-Migrants

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

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

  3. 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 • 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 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%

  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 MigrantsLondon 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-migrantsGrouping 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…

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