Data comparability over time
The broad picture of population change can be followed from census to census. But changes are made at each census to keep up with changes in society. These changes include the questions asked, the categories used to present results, and geographical boundaries.
Census to census changes mean that each census primarily provides a 'cross-sectional' picture of the country at the time it was taken, and that the censuses do not necessarily give a good source of information about detailed change over time.
Elements of continuity may nevertheless be found, for example the boundaries of local government areas in England have not changed substantially between 1981 and 2001, after wholesale reorganisation in 1974. Figures of population change were provided in the reports on local areas, but this information was cut back in the 2001 reports.
Chapter 4 of the Census 2001: Definitions volume provides a guide to the comparability of the 1991 and 2001 UK censuses in terms of questions, concepts and definitions. A comprehensive and striking picture of change between 1991 and 2001 can be seen in 'People and places: A 2001 Census Atlas of the UK' by Daniel Dorling and Bethan Thomas, The Policy Press (University of Bristol), 2004, ISBN 1 86134 555 0.
The range of questions asked has generally increased with each census. For a summary of the topics covered by questions in successive censuses, see census topics 1801-2001.
