Vital Statistics GIS Methodological Note
The Standardised Mortality Ratios (SMRs) by broad cause and sex for 1991 and 2001 were calculated as follows:
The SMRs were calculated using the 'indirect' method. The SMRs for local authorities (LAs) for 1991 were in relation to 1991 Age-Specific Mortality Rates (ASMRs) for England and Wales. The SMRs for local authorities (LAs) for 2001 were in relation to 2001 ASMRs for England and Wales.
The 'Populations at Risk' used were the Office for National Statistics (ONS) subnational estimates for 1991 and 2001 revised in the light of the 2001 Census.
The mortality 'event' counts by broad cause and sex were obtained from the Vital Statistics for 1991 and 2001. The ICD9 codes of the 1991 broad causes of mortality used were as close as possible to the equivalent ICD10 codes in 2001. Since 1991 mortality at LA level was being compared with 1991 national mortality by the ICD of that year, and similarly for 2001, adjustment using the sex-specific comparability ratios for the change to ICD10 was not applied.
The geography of local government changed between 1991 and 2001 so that the areal extent of a particular LA can have altered. The raw event counts for males and females were adjusted from the 1991 boundary definitions using the distribution of 1991 residential postcodes linked to the 2001 district boundaries and weighted by household counts. The method used is defined by:
Norman, P., P. Rees and P. Boyle (2003) "Achieving data compatibility over space and time: creating consistent geographical zones," International Journal of Population Geography Vol 9, Issue 5, September-October 2003: 365-386.
Simpson, L. (2002) "Geography conversion tables: a framework for conversion of data between geographical units," International Journal of Population Geography 8: 69- 82.
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