Every effort was made to ensure everyone was counted in the 2011 Census, however no census is perfect and some people were inevitably missed. This under enumeration does not usually occur uniformly across all geographical areas or across other sub-groups of the population such as age and sex groups.
To fill this gap, ONS developed a coverage assessment and adjustment methodology which built on the 2001 ‘One Number Census’ (ONC) approach. The methodology involved the use of standard statistical techniques, similar to those used by many other countries, for measuring the level of undercount in a census and providing an assessment of the characteristics of individuals and households missed. The approach was researched and developed over a number of years in consultation with academics, statisticians, demographers and users of census data.
An independent review of the coverage assessment and adjustment methodology took place in 2011. The review team stated that “the methods give confidence that the resulting final census population estimates will be better than any other method and will be suitable for use in resource allocation and planning”.