The One Number Census project identified the extent of under-enumeration (that is the number of people and households not counted) in the 2001 Census by conducting a large post-enumeration survey (the Census Coverage Survey). The people identified as not counted were imputed to produce an adjusted total on which the final Census results were based. Imputing these people met users' needs for a complete count, and reduced bias in the results due to any differences between the characteristics of respondents and non-respondents.
The numbers of people in each Local Authority, Ward and Output Area that were imputed into the final counts were used to produce an imputation rate. This rate has been used to produce a set of quality indicators. Quality indicators have been produced in the same way for each Strategic Health Authority, Primary Care Trust and Health Board.
The quality indicator consists of a four-point scale, relating to the proportion of imputed people in an area. The scale used is shown here:
Less than 5%
5% and less than 10%
10% and less than 20%
20% and over
Only residents in private households were considered when calculating the imputation rates, as no people were imputed into communal establishments by the One Number Census process. Students not at their term-time address have also been excluded from these counts.
The imputation rates used to calculate the quality indicators are a measure of the imputation of whole people. Another quality indicator is item response, part of the Edit and Imputation project, which imputed values for people who had made an incomplete return or whose answers were inconsistent. Again, this ensured that any differences in the characteristics of people who left particular questions blank were eliminated. Further information on the Edit and Imputation project can be seen HERE, and question non-response rates for each local authority are shown HERE.
Another aspect of quality is the existence of clusters of unprocessed forms in 16 local authorities. A list of these local authorities affected, together with estimates of the numbers of people and households missed, is available HERE.
The quality indicators (including information on unprocessed forms where relevant) for each local authority in England and Wales are accessible below. Each Local Authority contains a number of wards, which in turn contain a number of Output Areas.
Output Areas are small area building bricks for the release of 2001 Census results, and for use more widely in Neighbourhood Statistics. The vector (re-usable) boundaries for the 175,434 Output Areas in England and Wales are available without charge from Census Customer Services in two forms for users who wish to set up the boundaries in their own Geographical Information Systems. Further details can be found HERE.
The quality indicators for areas within each Strategic Health Authority in England and for each Health Board in Wales are also accessible below. Each Strategic Health Authority contains a number of Primary Care Trusts.
Browse for England and Wales Local and Health Authorities: