2001 census

Introduction
Data products
Related documents

Introduction

The 2001 Census of Population was conducted on 29 April 2001 and represents the 200th anniversary of census-taking in the UK. The census questionnaire forms the basis for a wide range of data products which are foundational to many aspects of academic research, public administration and commercial decision-making. Computer-readable datasets are available from 1971 onwards and more detail is generally available for more recent censuses.

Separate simultaneous censuses were conducted by the three government census agencies in the UK (the Office for National Statistics in England and Wales; the General Register Office for Scotland in Scotland and the Northern Ireland Statistics and Research Agency in Northern Ireland), and these form the basis for an extensive series of published outputs. These take the form of printed reports and major computer-readable datasets.

The data collected was scanned and encoded in anonymised form (without respondents' names and addresses) to form the census database. Subsequent to data collection, a major Census Coverage Survey was undertaken in order to inform a process known as the One Number Census, involving the statistical imputation of households and individuals judged to have been missed by the census enumeration. From the corrected census database, a full range of data products are produced.

Data products

Census area statistics (CAS) comprise counts aggregated to various sets of geographical units of which the smallest are census output areas, with a target size of 125 households (in England and Wales).

Digitised boundary data (DBD) are computer representations of the co-ordinates of the boundaries of the geographical areas for which census data are published.

Interaction data describe flows of people between places. One set describes journeys to work within and between all areas, and a second set describes migration flows, based on the census question concerning usual address one year prior to the census.

Samples of anonymised records (SARs) provide anonymised records for small samples of households and individuals but with only a coarse level of geographical referencing.

The ONS Longitudinal Study of England and Wales (LS), The Scottish Longitudinal Study (SLS) and The Northern Ireland Longitudinal Study (NILS) are major Longitudinal Studies which link a sample of full 2001 census records, with other censuses and major events in the lives of sample members.

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Censuses questions and forms