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

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

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

Factors available in the model 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. 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

Sex ratios – Out Migrants London vs. Non London

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.

International Out Migration Age Distribution

International Migration (IPS) age profiles

Allocation of British / Non British

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

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

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