Population health across space & time: geographical harmonisation of the ONS Longitudinal Study for England & Wales

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1 British Society for Population Studies Annual Conference, York, September 2011 Population health across space & time: geographical harmonisation of the ONS Longitudinal Study for England & Wales Paul Norman & Mylène Riva Centre for Spatial Analysis & Policy, School of Geography, University of Leeds Institute of Hazard, Risk and Resilience, Department of Geography, University of Durham (Axe Santé des Populations et Environnement Centre de Recherche du CHUQ Université Laval, Québec, Canada) Acknowledgements ONS LS data: Chris Marshall & CeLSIUS, a service funded by ESRC & ONS Microdata Analysis User Support: Final Clearance of results The research uses National Statistics Postcode Directory and GIS boundary data obtained via EDINA UKBORDERS an academic service supported by ESRC and JISC The Census and National Statistics Postcode Directory have been provided by ONS and the digital boundary data by OS. Data are Crown copyright and reproduced with the permission of the controller of HMSO and Queen's printer for Scotland and OPSI Geographical harmonisation? You're the Cheshire cat, aren't you? I was the Cheshire cat, he replied with a slightly aggrieved air, but they moved the county boundaries, so technically speaking I'm now the Unitary Authority of Warrington Cat, but it doesn't have the same ring to it. (p. 164) Fforde, Jasper (2002) Lost in a good book. Hodder & Stoughton:

2 Population health across space & time: Geographical inequalities in health over time Specific places: Regions, North-South, etc Generic types: deprivation, urban-rural, geodemographic Outcome for individuals modelled in relation to area types in which people lived through their life course Time-series of cross-sections or start-end comparison of survivors aggregated across area types Investigating inequalities hampered by definitional changes Health outcome measures Sociodemographic data specification Geographical zone systems Geographical harmonisation of the ONS LS for England & Wales Health-related variables Census: Permanently sick ( ), Limiting Long- Term Illness (1991 & 2001, General Health (2001) Mortality: All cause & by ICD Cancer registrations Geography related variables Census, health, functional Area types: deprivation, urban-rural, geodemographic Time-point specific Any change hampers time-series or longitudinal analysis

3 Health geography change? The redisorganisation of the NHS Smith J, Walshe K, Hunter D (2001) BMJ: 323: Soon All change!! Census LA geography change? 1971 Skipton Urban & Rural Districts 1981 Craven District 1991 Craven District 2001 Craven District

4 Census ward geography change? 1971 Skipton 1981 Skipton 1991 Skipton 2001 Skipton Census geography: availability in LS? Nation (England & Wales) Government Office Region Local Government Ward Super Output Areas LS Info exists but not always available for analysis Output Area (OA) Re: 2001, different at other time points Enumeration Districts (EDs) have been smallest geography

5 Linking LS geographies? 1971 Census 1981 Census 1991 Census 2001 Census Ward >16,000 ED Wards 9,289 ED Wards 9,527 OA Wards 8,850 For an LS member living in a particular ward in 1971, what 2001 OA would that be? Following slides NOT using the LS Linking (LS) geographies? Postcode points used to link geographies (Simpson 2002; Norman at al., 2003) Within any polygon, population-weighted centroid best represents a single location for linkage Address-weighted postcode locations estimates centroid

6 Linking (LS) geographies Skipton, 1991 Enumeration Districts & postcode distribution Skipton, 1991 EDs Geometric (x) & population-weighted ( ) centroids Linking (LS) geographies Skipton, 2001 OAs 1991 ( ) & 2001 (+) population-weighted centroids

7 Linking LS geographies Supply series of lookup tables 1971 District 1971 Ward 1971 Code 2001 Output Area Easting Northing SKIPTON UD NORTH LS UBGP SKIPTON UD WEST LS UBGQ SKIPTON UD CENTRAL LS UBGR SKIPTON UD EAST LS UBGR SKIPTON UD SOUTH WEST LS UBGS SKIPTON UD SOUTH LS UBGS If in 1971 an LS member lived in Skipton North Ward, then most likely this would be 36UBGP0010 in 2001 Most likely, but not necessarily Degree of hierarchy Degree of fit 1971 to 2001 Geography 1981 to 2001 Geography % Degree of fit or hierarchy OA LSOA Ward District % Degree of fit or hierarchy OA LSOA Ward District Degree of Hierarchy Degree of Fit Degree of Hierarchy Degree of Fit

8 Time-series using LS: mortality (aged <65) Age Standardised Death Rates (per 100,000) Mining & Manufacturing Cosmopolitan Cities & Services Coastal & Countryside Centre Prospering UK Suburbs Longitudinal using LS: LLTI in Standardised Illness Ratios in Mining & Manufacturing Cosmopolitan Cities & Services Coastal & Countryside Centre Prospering UK Suburbs

9 Summary Administrative boundary change hampers time-series & longitudinal analyses Established longitudinal and cohort studies can recover geographical consistency by estimating contemporary geographies for old records Smaller source units are better & Reliability of linkage improves with increasing unit size Studies should retain postcodes Otherwise, population-weighted centroids of smallest available geographical area provide linkages to alternative geographies Supply lookup table to CeLSIUS with link to OA or higher 2001 geography with your own geography or typology Geographical names may change but the sign remains the same! Footpath sign in Skipton S.U.D.C. = Skipton Urban District Council Located at: National Grid Reference , In 1971 in Central Ward in Skipton Urban District, West Riding of Yorkshire (but pre-1974 might not have had a postcode) To date, at least 4 ward boundary change, 1 district change, 1 county change Smallest geography different every census Health geography, at least 8 changes

10 References Boyle P, Norman P & Rees P (2004) Changing places: do changes in the relative deprivation of areas influence limiting long-term illness and mortality among non-migrant people living in non-deprived households? Social Science & Medicine 58: Norman P & Riva M (2010) Population health across space and time: the geographical harmonisation of the ONS Longitudinal Study for England and Wales. Population, Space & Place (submitted) Norman P, Boyle P & Rees P (2005) Selective migration, health and deprivation: a longitudinal analysis. Social Science & Medicine 60(12): Norman P, Rees P & Boyle P (2003) Achieving data compatibility over space and time: creating consistent geographical zones. International Journal of Population Geography. Vol 9, Issue 5, September-October 2003: Simpson, L. (2002). Geography conversion tables: a framework for conversion of data between geographical units. International Journal of Population Geography 8: 69-82