The One Number Census process involved a number of stages:
a Census Coverage Survey was designed and conducted independently of the census during May/June 2001;
records from the CCS were matched to those from the 2001 census;
populations of the sample areas were estimated from the results of the matching using dual system estimation techniques which enabled an estimate of those persons missed by both the census and the CCS to be made;
populations for each local authority by age and sex were then estimated using a combination of standard regression and small area estimation techniques;
households and persons estimated to have been missed by the census were then imputed to produce a fully adjusted census database; and finally
all population estimates were carefully quality assured using demographic analysis and comparison with aggregate level administrative data.
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