Appendix A

Sources and methods

This appendix briefly discusses the data sources and methods used by the authors of this volume. A guide to the maps and details on the geography used are also included. Generally this appendix only discusses issues that are relevant to more than one chapter to avoid duplication between individual chapters.

Data sources

A wide variety of sources have been used in this volume, including birth and death registration data, cancer registration data, abortion notifications and congenital anomaly notifications. More details on these data sources can be found within the relevant chapters. These sources have been supplemented, where possible, using data from the ONS Longitudinal Study, and the introductory chapters make use of both Census and survey data.

The ONS Longitudinal Study

The ONS Longitudinal Study (LS) is a representative one per cent sample of the population of England and Wales containing linked Census and vital events data for approximately 500,000 people. The LS was begun in the early 1970s by selecting everyone born on one of four particular dates who was enumerated at the 1971 Census. Subsequent samples have been drawn and linked from the 1981 and 1991 Censuses using the LS dates of birth and data from the 2001 Census will also be linked. Population change is reflected by the addition of new sample members born on the LS dates together with the recording of exits via death or emigration. Routinely collected data on mortality, fertility and cancer registration for sample members are linked using the National Health Service Central Register (NHSCR) to perform the link. More details on the LS can be found in the LS Technical Volume.1

 

Methods

Method of age-standardisation

All rates in chapters 9-12 of this volume are age-standardised. Mortality and cancer incidence increase with age and therefore areas with older populations would generally experience higher crude rates than those with young populations. Age standardisation enables comparisons of mortality and cancer incidence rates between different areas while allowing for differences in the age structure of the population. All mortality and cancer rates in this volume are directly standardised using the European Standard Population (Table A1). This is used because it is closest to the demographic profile of the United Kingdom, having a high proportion of the population in the older age groups. The same population is used for both males and females. Directly standardised rates measure the number of events per 100,000 population that would occur in the standard population if it had the same age-specific rates as the population being studied. Further details of direct standardisation can be found in numerous demography and statistical textbooks.2, 3

Defini tio ns

ASR Directly age-standardised rate per 100,000 using the European standard population.
CIR  Comparative incidence ratio: the ratio of the region ASR and the ASR for the United Kingdom multiplied by 100.

Calculation of confidence intervals

  Standard methods for the calculation of the confidence interval for a directly standardised rate are used.2, 3 All confidence intervals for data for countries and regions have been calculated at the 95% level, using the appropriate methods for the rate or percentage under discussion. Where necessary, further details have been discussed within individual chapters. All confidence intervals for local authorities used in the presentation of maps have been calculated at the 90% level.