1. IAOS 2008 - Shanghai – Reshaping Official Statistics Some Initiatives on Combining Data to Support Small Area Statistics and Analytical Requirements at ONS-UK Denise Silva and Philip Clarke

2. 2 Outline Small Area Estimation (SAE) problem SAE history at ONS Successful ONS experiences on Small Area Estimation Small Area Estimation Project (SAEP) and the production of income estimates Small area estimation for the 2001 Census Small Area estimates for unemployment Lessons learned Developments in progress Preparing for future challenges

3. 3 Small Area Estimation Problem NSIs challenge: to produce reliable information under operational constraints Pressure for reducing sample sizes and respondent burden Data requested for small areas or domains but limited resources for data collection In sample surveys: sample sizes not large enough to provide reliable estimates for small areas Solution: borrow information from other related datasets – from similar areas – from previous occasions

4. 4 Small Area Estimation Methods Methods for producing small area statistics from combined data sources –Rely on statistical models that relate survey data with auxiliary information –Auxiliary information: administrative data or census data Modelling procedure fitted using sample data –Dependent variable is survey variable of interest –Independent variables are auxiliary data (covariates)

5. 5 1993199419951996199719981999 ONS = OPCS+CSO In the beginning… OPCS + IoE projects: experimental studies on mental health estimation for DoH OPCS commissioned UoS to examine potential for small area estimation

6. 6 1993199419951996199719981999 ONS: Small Area Estimation Project (SAEP) - research First OPCS + UoS report Small Area Estimation Projects Timeline ONS initial experiments Eurostat project: ONS, Statistics Finland + 2 Universities

7. 7 1993199419951996199719981999 First OPCS + UoS report SAEP Small Area Estimation Projects Timeline ONS initial experiments 2001 Census tests: small area population estimates

8. 8 200020012002200320042005200620072008 2001 Census Implementation Small area estimates of unemployment : research 2001-2004: EURAREA research project NSIs + Universities 7 European Countries Small Area Estimation Projects Timeline

9. 9 200020012002200320042005200620072008 2001 Census + research on small area estimates of income and unemployment Implementation stage: estimates of income and unemployment + current developments Small Area Estimation Projects Timeline Model based estimates at small areas are accepted as a part of ONS established statistical outputs

10. 10 Framework for small area estimation at ONS Successful experiences in social statistics: –estimates for income, unemployment and population (2001 Census) Auxiliary information from Census and from administrative databases available at aggregated levels Incompatible and changing boundary systems –variety of geographic unit types –boundaries do not always align

11. 11 The SAEP methodology and income estimation Estimates published for 1998/99, 2001/02 and 2004/05 at local area level ( 7100 small areas) Survey data: mean household income from Family Resources Survey Auxiliary data: Census variables, social benefit claimants, council tax banding, house sale price index and Income tax data Linear regression for log income with area random effect Model with unit level response and area level covariates

12. 12 ILO unemployment measured by the Labour Force Survey (LFS) - the direct estimates LFS has unclustered survey design – giving a sample in each Local Authority ( 400 areas) Small sample sizes at Local Authority (LA) level Use job seekers allowance claimant count as auxiliary data Small area estimation of unemployment level and rates for Local Authorities in GB

13. 13 Estimation of unemployment at Local Authority level Survey data: number of respondents by age/sex group in each LA who are unemployed from LFS –age groups: 16 to 24; 25 to 49; 50 and over Auxiliary data: job seekers allowance claimant counts + geographical region + ONS area classification Area level model by age/sex groups in each LA Binomial mixed model with a logistic link function Model relates the probability of an individual in age-sex group be unemployed within each LA to the auxiliary data

14. 14 Small area estimation for the 2001 Census Key elements/stages of the One Number Census: –the Census itself –the Census Coverage Survey (CCS) –the matching of Census and CCS to estimate undercount – the process to obtain model based population estimates for Local Authorities –the production of a database with individual and household level records

15. 15 Small area estimation for the 2001 Census Survey data: –Census Coverage Survey (CCS) count Auxiliary data: unadjusted census count simple linear regression model through the origin with different coefficients (slopes) across Local Authorities Area level model

16. 16 Lessons learned Good small area estimates depend on: –adequacy of the modelling procedures –covariates with good prediction power –model validation prior to publication Big effort to transfer to the production area

17. 17 Lessons learned Challenges: –ability to master complexities of statistical theory –availability of relevant auxiliary data –acceptance of model based estimates as official statistics outputs

18. 18 When we find the answers…. they change the questions Labour Market area Unemployment estimation at Parliamentary Constituency Area (PCA) level –Local Authority and PCA are non-nested geography –Boundaries change over the years –Issue is to ensure consistency with LA estimates at comparable areas Consistent estimation of all three labour market states: employed, unemployed and not economically active

19. 19 When we find the answers…. Income estimation –Income distribution each area –threshold value defined as 60% of national median income (also considered as a poverty line) –SAEP methods can be used to estimate proportion of households below the poverty level

20. 20 When we find the answers…. Other projects (in earlier stages ) –Small area estimation for business surveys –Statistical models to improve international migration small area statistics Research projects (with academic consultants) –Small area estimation of income distribution –Estimation of change over time ONS committed to quality whilst responding to users’ requirements

21. 21 Looking forward The more successful we are in obtaining small area estimates… the more complex the estimation system becomes Need to ensure: –comparability over time –consistency over area/domains –coherence over variables More general issues –Analysis of change over time –Broader areas estimates and precision measures

22. 22 Preparing for future challenges For producing statistics from combined data sources –Methodology Directorate established strategy for developing data matching and data sharing Investigate models to improve comparability over time and consistency over geographies Need to experiment with resampling methods for calculating precision of the estimates

23. 23 THE END For references: see paper "Data! data! data!" he cried impatiently. "I can't make bricks without clay." So said Sherlock Holmes to Dr. Watson in "The Adventure of the Copper Beeches" (by Sir Arthur Conan Doyle)