Mismatches and matches in address information from the Census and the BSO: A longitudinal perspective Ian Shuttleworth and Brian Foley, Queen’s University Belfast British Society for Population Studies annual conference 9 th September 2015, University of Leeds

Presentation format Context Data source, research approach and methods Backdrop of societal change in Northern Ireland (NI) during the 2000s Research questions Results Summary and conclusions

Context Shift in approach to future production of UK population statistics Greater use of administrative data sources  enhance quality of statistical outputs from 2021 Census Post-2021; move away from traditional census-taking approach Health service registration data - fundamental role  important to improve understanding of data quality  research focus → accuracy of address information

Data source Northern Ireland Longitudinal Study (NILS)  representative 28% sample (circa 500,000 individuals)  health card registration data from Business Services Organisation (BSO)  one of 104 designated birth dates Linked to census and vital events data Address information for NILS members updated through six- monthly data downloads provided by BSO

Research approach Assess quality of address information in NI health card registration data over time Cross-sectional comparison of address Super Output Area (SOA) from linked health card registration and census records 2001 Census BSO health card registrations, April 2001 SOA of address 2011 Census BSO health card registrations, April 2011 SOA of address NILS

Methods Descriptive statistics on rates of address match/mismatch in 2001 and 2011, based on all ages Multilevel logistic regression modelling  binary outcome variable (1 = SOA mismatch, 0 = SOA match)  hierarchical data (individuals nested within SOAs)  based on age group with SOA recorded in both the health card registration and census data  circa 315,000 and 347,000 records for 2001 and 2011, respectively

Change in NI during the 2000s Advances in information technology Ageing population Expansion of rental sector Increase in migrant population

Demographic and socio-economic change Population Population by age band Source: Northern Ireland Statistics and Research Agency (NISRA)

Demographic and socio-economic change Country of birth Long-term migration Source: NISRA

Demographic and socio-economic change Housing tenure Education Source: NISRA

Research questions How do the rates and geography of address mismatch in health card registration data in 2011 compare with the situation in 2001? What is the descriptive profile of address match/mismatch in 2011 and how does this compare with the situation in 2001? Has the association between address mismatch and relevant individual-, household- and area-level variables changed between 2001 and 2011? What is the transition in address match/mismatch status of NILS members between 2001 and 2011?

Address accuracy status n = 456,290n = 485,185 Address match Address mismatch SOA missing in health card registration data Source: NILS

Address mismatch rate, 2001 Belfast Source: NILS

Address mismatch rate, 2011 Belfast Source: NILS

Research questions How do the geography and rates of address mismatch in health card registration data in 2011 compare with the situation in 2001? What is the descriptive profile of address match/mismatch in 2011 and how does this compare with the situation in 2001? Has the association between address mismatch and relevant individual-, household- and area-level variables changed between 2001 and 2011? What is the transition in address match/mismatch status of NILS members between 2001 and 2011?

Address mismatch by age Source: NILS

Sex Marital status Address match Address mismatch SOA missing in health card registration data 0% 50% 100% Source: NILS

Limiting long- term illness Education Address match Address mismatch SOA missing in health card registration data 0% 50% 100% Source: NILS

Country of birth Address one year ago Address match Address mismatch SOA missing in health card registration data 0% 50% 100% Source: NILS

Tenure Accommodation type Address match Address mismatch SOA missing in health card registration data 0% 50% 100% Source: NILS

Research questions How do the geography and rates of address mismatch in health card registration data in 2011 compare with the situation in 2001? What is the descriptive profile of address match/mismatch in 2011 and how does this compare with the situation in 2001? Has the association between address mismatch and relevant individual-, household- and area-level variables changed between 2001 and 2011? What is the transition in address match/mismatch status of NILS members between 2001 and 2011?

Sex (ref cat: Male)Female Age (ref cat: yrs)25-34 yrs yrs yrs yrs yrs Marital status (ref cat: Single)Married Separated Divorced Widowed Limiting long-term illness (ref cat: Yes)No Qualifications (ref cat: No)Yes Religion (ref cat: Catholic)Protestant & other Christian Other religions Country of birth (ref cat: UK/Ireland)Non-UK/Ireland NSSEC (ref cat: Professional)Intermediate Routine Student Address one year ago (ref cat: No move)Moved from within UK Moved from outside UK Tenure (ref cat: Owner occupied)Social rented Private rented Communal 2001 Population density, Log 10 scale Quartile 2 (ref cat: Quartile 1) Quartile 3 Quartile Deprivation Score, Log 10 scale Quartile 2 (ref cat: Quartile1) Quartile 3 Quartile 4 Between-SOA variance: null model 0.21, specified model ,204 Level 1 units, 890 Level 2 units Lower odds Higher odds Binary logistic multilevel model: 2001 Source: NILS

Sex (ref cat: Male)Female Age (ref cat: yrs)25-34 yrs yrs yrs yrs yrs Marital status (ref cat: Single)Married Separated Divorced Widowed Limiting long-term illness (ref cat: Yes)No Qualifications (ref cat: No)Yes Religion (ref cat: Catholic)Protestant & other Christian Other religions Country of birth (ref cat: UK/Ireland)Non-UK/Ireland NSSEC (ref cat: Professional)Intermediate Routine Student Address one year ago (ref cat: No move)Moved from within NI Moved from outside NI SOA (mis)match status 2001 (ref cat: Matching)Mismatched SOA missing in BSO data Tenure (ref cat: Owner occupied)Social rented Private rented Communal 2011 Population density, log scaleQuartile 2 (ref cat: Quartile 1)Quartile 3 Quartile Deprivation Score, log scale Quartile 2 (ref cat: Quartile 1) Quartile 3 Quartile 4 Between-SOA variance: null model 0.12, specified model ,617 Level 1 units, 890 Level 2 units Lower odds Higher odds Binary logistic multilevel model: 2011 Source: NILS

Research questions How do the geography and rates of address mismatch in health card registration data in 2011 compare with the situation in 2001? What is the descriptive profile of address match/mismatch in 2011 and how does this compare with the situation in 2001? Has the association between address mismatch and relevant individual-, household- and area-level variables changed between 2001 and 2011? What is the transition in address match/mismatch status of NILS members between 2001 and 2011?

Transition in address match/mismatch status n = 371,998 Source: NILS

Summary of main findings Increase of circa 2% in the address mismatch rate in 2011 Highest rates of address mismatch in urban areas in both years Descriptive profile of address match/mismatch very similar in 2011 compared to 2001 High odds of address mismatch in 2011:  male  25 to 34 age group  moved in the year before the census  address mismatch in 2001  private renters  more densely populated areas

Conclusions Despite demographic and socio-economic change in NI, address mismatch situation in 2011 similar to that in 2001 Conservative estimate of address mismatch Implications for sub-national population estimates and other statistics they underlie, e.g. health and economic indicators Increasingly mobile population → difficult to reference individuals to a single address

Future analysis Further analysis of NILS members exhibiting address mismatch in both 2001 and 2011 Use subsequent downloads of BSO data after April 2011 to investigate the lag in updating of address information in health card registration data to match that recorded in the 2011 Census Undertake the analysis using Unique Property Reference Number, which will provide an insight into mismatch at the individual address level

The help provided by the staff of the Northern Ireland Longitudinal Study and the NILS Research Support Unit is acknowledged. The NILS is funded by the Health and Social Care Research and Development Division of the Public Health Agency (HSC R&D Division) and NISRA. The NILS-RSU is funded by the ESRC and the Northern Ireland Government. The authors alone are responsible for the interpretation of the data and any views or opinions presented are solely those of the author and do not necessarily represent those of NISRA/NILS. NILS-RSU Contact Details: Acknowledgement

Characteristics of NILS members with address mismatch in both 2001 and 2011