Aims

1. Constructing population time series with an ethnic breakdown (and age and sex) for sub-national areas in England and Wales, 1991-2001 Albert Sabater, PhD student at Cathie Marsh Centre for Census and Survey Research University of Manchester albert.sabater@postgrad.manchester.ac.uk Supervision: Ludi Simpson and Paul Norman

2. Constructing population time series with an ethnic breakdown (and age and sex) for sub-national areas in England and Wales, 1991-2001 Aims • Create consistent population time series with an ethnic breakdown (and age and sex) for a variety of sub-national areas -Districts, wards, smallest census areas and new areas • Analyse population change of ethnic groups in E&W

3. Constructing population time series with an ethnic breakdown (and age and sex) for sub-national areas in England and Wales, 1991-2001 Background Census output from both 1991 and 2001 provides detail of the population by age, sex and ethnic groups BUT... Analyses of population change are restricted for sub-national areas by four separate problems: 1. Changes in the population definition -Enumeration of students -Timing adjustment 2. Different treatment of undercount 3. Differences in ethnic group categories 4. Boundary changes

4. Constructing population time series with an ethnic breakdown (and age and sex) for sub-national areas in England and Wales, 1991-2001 Approaches to harmonise census time series -Linking Censuses Through time (LCT) http://census.ac.uk/cdu/software/lct/ (Martin, Dorling and Mitchell, 2002) • Data linked: 1981-1991-2001 Censuses • Geographies: wards and levels above in E&W and Scotland • Includes an allowance of non-response, correction for students and timing transfer (census to mid-year) • Ethnic groups: White, Asian, Black and Other (3+1 residual) • Not cross-tabulated by age and sex An example of analysing population change by ethnic groups using LCT: Rees and Butt (2004) Ethnic change and diversity in England, 1981-2001

5. Constructing population time series with an ethnic breakdown (and age and sex) for sub-national areas in England and Wales, 1991-2001 Strategy -Changes in the population definition and -Different treatment of undercount Solution 1: use of complete mid-year population estimates derived form the latest 2001 Census results -Differences in ethnic group categories Solution 2: take into account ‘best fit’ categories -Boundary changes Solution 3: use of Geographical Conversion Tables (GCT)

6. Constructing population time series with an ethnic breakdown (and age and sex) for sub-national areas in England and Wales, 1991-2001 Solution 1: use of complete MYEs Iterative Proportional Fitting (IPF) is used to scale census counts to revised mid-year population estimates derived from 2001 ONC IPF method: the original table values are gradually adjusted through repeated calculations to fit row and column constraints More detail but less reliable ORIGINAL TABLE ROW CONS COLUMN CONSTRAIN Less detail but more reliable

7. Constructing population time series with an ethnic breakdown (and age and sex) for sub-national areas in England and Wales, 1991-2001 An example Original table Amended table Cross-product ratio: (8/2)/(8/2) = 1 Age-sex pattern does not change Cross-product ratio: (10/3)/(10/3) = 1

8. Constructing population time series with an ethnic breakdown (and age and sex) for sub-national areas in England and Wales, 1991-2001 Large datasets -IPF implemented in SPSS using GENLOG command (Simpson and Tranmer, 2003)

9. Constructing population time series with an ethnic breakdown (and age and sex) for sub-national areas in England and Wales, 1991-2001 Solution 2: matching ethnic groups -Dorling and Rees (2003) -Thomas and Dorling (2004) -Simpson, Platt and Akinwale (2005)

10. Constructing population time series with an ethnic breakdown (and age and sex) for sub-national areas in England and Wales, 1991-2001 Solution 3: geographical conversion tables (GCTs) Boundary change 1991 2001 Source geography Target geography No (direct allocation) Yes (multiple allocation) Yes (multiple allocation with intersection) Area 1 Zone 1 Area 2 Area 3 Zone 2 Area 4 Weight *0.5 *0.5 Zone 3 Area 5 Zone 4

11. Constructing population time series with an ethnic breakdown (and age and sex) for sub-national areas in England and Wales, 1991-2001 Solution 3: an example of GCT Direct allocation Multiple

12. Constructing population time series with an ethnic breakdown (and age and sex) for sub-national areas in England and Wales, 1991-2001 % Adjustment 2001 census-mid-year Check? From 2001 Districts Timing adjustment Non-response adjustment

13. Constructing population time series with an ethnic breakdown (and age and sex) for sub-national areas in England and Wales, 1991-2001 References -Dorling, D and Rees, P (2003), A nation still dividing: the British census and social polarisation 1971-2001, Environment and Planning A, 35, 1287-1313. -Martin, D; Dorling, D and Mitchell, R (2002), Linking censuses through time: problems and solutions, Area, 34, 1, 82. -Norman, P (1999), Putting iterative proportional fitting on the researcher’s desk, Working Paper 99/3. School of Geography, University of Leeds. -Rees, P and Butt, F (2003), Ethnic change and diversity in England, 1981-2001, Area, 36, 2, 174. -Simpson, L and Tranmer, M (2003), Combining sample and census data in small area estimates: Iterative Proportional Fitting with standard software, Professional Geographer, 57, 2, 222-234. -Simpson, L; Platt, L and Akinwale, B (2005), Stability and change in ethnic group in England and Wales, Population Trends, 121. -Thomas, B and Dorling, D (2004), Endpiece: mapping changes and the 2001 census for the UK. Area 36 (2, CD and web version).

14. Constructing population time series with an ethnic breakdown (and age and sex) for sub-national areas in England and Wales, 1991-2001 Albert Sabater, PhD student at Cathie Marsh Centre for Census and Survey Research University of Manchester albert.sabater@postgrad.manchester.ac.uk Supervision: Ludi Simpson and Paul Norman