Improved Methods for Population and Migration Estimates ONS Centre for Demography May 2007

1. Improved Methods for Population and Migration EstimatesONS Centre for Demography May 2007

2. Improved population statistics methods in 2007 • ONS is planning to make improvements in 2007 to the methods for distribution of the national population estimates to local areas. • These principally concern how long term international migrant numbers are distributed locally

3. Improvements being implemented in Population Statistics in 2007 • Improved distribution of international in-migrants • Improved distribution of international out-migrants • Improved assumption setting on proportion of people who change their intentions on length of stay (‘switchers’)

4. Improvements being implemented in Population Statistics in 2007 • Improved distribution of international in-migrants: • Between England & Wales and between regions of England • From regions to local authority level (LAs) using 2 stage process via improved intermediate level geography • Improved age distribution of in-migrants • Improved distribution of international out-migrants: • Between LAs using 2 stage process from regions to LAs via improved intermediate level geography • Improved age distribution of out-migrants • Improved assumption setting on proportion of people who change their intentions on length of stay

5. ONS wider work programme on population statistics • This work is part of ONS wider work programme on population statistics, which aims to • Improve population estimates between Censuses as well as the 2011 Census-based estimates, • minimise the risk of divergence between Censuses • providing a better understanding of the differences that remain between the Census and rolled forward estimates

6. Further improvements to population statistics • Increased sample size of out-migrants in International Passenger Survey in January 2007 • Reporting the recommendations of the Task Force on International Migration • Review of port surveys • Use of administrative data in population estimation • Researching feasibility of estimating short term migration • Reporting on two of four Local Authority Case Studies that started at the end of 2005

7. Timetable for improvements in 2007 • Population estimates, based on the revised methods will be released in August • first release of figures for 2006 • revised estimates for the years 2002-5 • Current sub-national population projections, based on the 2004 estimates, will be revised (September).

8. Timetable for further improvements • Products from this work will be made available as soon as they are completed. • No further revisions to existing population estimates will be made for at least two years.

9. Quality Assurance and Communication Methods were: • subject to rigorous QA during development • independent internal QA • discussed at CLIP • presented at conferences • external QA panel • May seminars explaining improvements and impacts

10. Improved Methods for Estimating International Migration Emma Wright, Jonathan Smith & Fiona Aitchison

11. Overview of Improvements • Improved geographical distribution of international in-migrants at: • Wales/GOR level Emma Wright • local authority level Jonathan Smith • Improved geographical distribution of international out-migrants at: • local authority level Fiona Aitchison • Improved estimation of people whose intentions change with respect to length of stay Emma Wright

12. Improved geographical distribution of international in-migrants at country/GOR level

13. International Passenger Survey (IPS) • Basis for estimates of long-term international migration • Continuous voluntary sample survey conducted at majority of UK ports • Airports, Sea Ports & Channel Tunnel • Migrants interviewed at the start of their stay – responses based on their intentions

14. Estimating Total International Migration Irish Flows Asylum Seekers Visitor Switchers IPS Migrants Migrant Switchers Total International Migration (TIM)

15. Labour Force Survey (LFS) • Large sample survey of 60,000 households per quarter; most communal establishments not sampled • International in-migrants identified as those resident overseas one year previously • Geographical location of in-migrants based upon actual place of residence

16. Census • Coverage of communal establishments as well as private households • International in-migrants identified as those resident overseas one year previously • Geographical location of in-migrants based upon actual place of residence

17. Proportion of UK immigrant inflows by UK countries/English regions, 2001

18. UK Country/English Region level:Comparison of IPS and LFS • Higher percentage of international in-migrants allocated to London in IPS: • consistent over time • greatest for young adult age-groups • Evidence from IPS and Longitudinal Study: • higher percentage of migrants intending to live in London state that they are likely to move on to a different area • migrants who move on quickly unlikely to be recorded in internal migration sources

19. UK Country/GOR level: Methodology • IPS and LFS data used in combination: • Distribution of in-migrants in LFS used to allocate IPS in-migrants at GOR/country level • Methodology developed: • worked at IPS-contact level and minimised changes to weightings • took account of London/non-London differences in distributions by age and sex • used three years’ LFS distributions for robustness

20. Change to country/regional distribution of in-migrants, mid-2004

21. Difference between existing and new geographical distributions

22. Improved geographical distribution of international in-migrants at Local Authority level

23. Existing Method Data/Methods Geographic Level North East Newcastle & N Tyneside Distributed to Local Authority using Census immigration

24. How are we improving distribution to LA? • ‘Central tendency’ within regions • Replace intermediate geography • Harmonise methods estimates/projections • Age distributions

25. Local area distribution of in-migrants: data sources considered • Surveys • International Passenger Survey • Labour Force Survey (LFS) • Census • Administrative Sources • Worker Registration Scheme (WRS) • National Insurance Numbers • Patient Registers

26. IPS Data – Central Tendency • Example of central tendency • Newcastle • Comparison between IPS and Census

27. Identifying Areas with a ‘Positive Central Tendency’

28. New Migration Geography In-migration (NMGi) • Positive central tendency LAs • Thirteen in total • Grouped with neighbouring LAs • Remaining LAs grouped - Sample size - Neighbouring LAs

29. New Method Overview – Outside London Geographic Level Data/Methods IPS Data at GOR North East Region 3 Year IPS average to NMGi NE1 NMGi Newcastle Census data to LA Local Authority Local Authority Newcastle In-Migration Controlled Control to New Regional Total

30. In-migration Within London IPS data • London – unique as a city and region • In-migration spread across London LFS data • Household survey – not intention based • Required to group LAs together • Foreign students in LFS

31. Migration Geography in London

32. New Method Overview - London Geographic Level Data/Methods London Non-Students London Students IPSData London 3 Year LFS average to NMGi LO2 Non-Students NMGi Brent Non-Students Brent Students Census data to LA Local Authority Brent In-Migration Combine Students & Non-Students Local Authority Brent In-Migration Controlled Control to New Regional Total Local Authority

33. Age Distribution • Current Method – National Age Distribution

34. Improving Age Distribution • Local Areas have different age profiles • Students • Workers • Joining friends/family • IPS data can’t be used directly – group LAs together • Census – Similar in-migrant age distributions

35. Final Age Distribution Examples - Females

36. Improved geographical distribution of international out-migrants at Local Authority level

37. Existing Method Previous year’s resident population used to apportion HA/FHSAs

38. Limitations with Existing Method • Method assumes that within the intermediate geography everyone is equally likely to migrate • Intermediate geography has too few sample points in many areas – especially NE and North generally • Intermediate geography is obsolete – health geography areas no longer used

39. Challenges to developing a new approach • Very limited sources/information on international out-migrants • Sample size is a big issue. • Sample size precludes direct estimation of migrants from IPS at LA level.

40. New Method Geographic Level Data/Methods

41. Examples of New Intermediate Geography: North East and South East Reading North Tyneside Newcastle upon Tyne Brighton and Hove Portsmouth

42. Propensity to Migrate Model • Used to apportion from intermediate geography to local authority level. • Uses model to predict the number of migrants per head of population. • Model uses linear regression • Forward Stepwise entry selection method • Consists of a number of socio-economic and demographic factors. • Model results in a significant improvement • The percentage of variance explained is increased • R2 increases from around 40% to over 80%

43. Example of the Model: 2005 • In 2005 the variables below are used to form the model, in addition to a constant term. • Estimated in-migrants • Females aged 10-14 • Persons in lower supervisory/technical occupations • Persons in Black ethnic group • Density: persons per hectare • The model results are then scaled to the total of the New Migration Geography area (NMGo).

44. Evaluation of Model • The Propensity to Migrate Model has been evaluated to ensure continuity over time • A number of different models have been evaluated • The variables included in the model will be re-assessed each year

45. Age distribution • Existing Method: Applies national age distribution to all LAs • New Method: Applies different age distributions to different types of LAs • LAs split into 2 groups • London areas and large towns • Other areas • Differences between British and Non-British citizen age profiles accounted for • Results constrained to national age distribution from IPS

46. Improved estimation of people whose intentions change with respect to their length of stay

47. Switchers: Background

48. Switchers: Background

49. Switchers: Background

50. Current Switcher Adjustments Migrant Switchers: • 5 per cent of IPS migrant inflows • 1 per cent of IPS migrant outflows Visitor Switchers: • Fixed proportions of intended long stay visitors • Different assumptions for EU and non-EU citizens