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Quality and methods

The census is the most complete source of information about the population that we have. Every effort is made to include everyone. It is the only survey which provides a detailed picture of the entire population, and is unique because it covers everyone at the same time and asks the same core questions everywhere. This makes it easy to compare different parts of the country.

However no census is perfect and some people are inevitably missed. ONS therefore uses complex statistical techniques to adjust the 2011 Census counts for those people missed by the census. The methods and quality assurance approach was researched and developed in consultation with academics, statisticians, demographers and users of census data. The result was a suite of methods to process, clean, adjust and protect the census results.


Includes quality assurance which ensures that the methods have been correctly applied and that the statistics are robust and fit for purpose; and quality measures which help users understand the quality of the 2011 Census results, alongside outline descriptions of the methodology whose success is being measured.

Also includes information about how census compares with other data sources. Find out more.


A description of the coverage assessment and adjustment methodology which compensates for under- and overcount, and the statistical disclosure control methodology which protects confidentiality. Find out more.


Content from the Office for National Statistics.
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