The One Number Census identified the extent of under-enumeration in the 2001 Census by conducting a large post-enumeration survey. The people identified as not counted were imputed to produce an adjusted total on which the final Census results were based. This met user needs for complete coverage, and reduced any bias in the results arising from differences between the characteristics of respondents and non-respondents.
Under-enumeration in the 2001 Census did not occur uniformly across all areas. The patterns of Census response were as expected, that is response rates were lowest for inner city areas where characteristics known to be related to Census non-response are most prevalent such as multi-occupancy and higher proportions of non-English speaking population.
The numbers of people and households imputed in each local authority into the final counts were used to produce an imputation rate, analysed by key variables. The following imputation rates are available:
Person imputation rates for each local authority and ward, for males and females
Person imputation rates for each local authority, by sex and the following variables: 5 year age group, marital status, ethnic group, activity last week, tenure, accommodation type, household composition, and household size
Household imputation rate for each local authority and ward
Household imputation rate for each local authority, by the following variables: tenure, accommodation type, household composition, and household size
Only residents in households were included in the calculation of the imputation rates, as no people were imputed into communal establishments by the One Number Census process. Students not at their term-time address were also excluded from calculations.
The imputation rates as described above are available in a separate file for each local authority. These can be found with other quality information specific to each authority in the Local Authority Data Quality section using the link above. Additionally, all imputation rates can be downloaded in a single zip file using the download link above.