ONS developed a coverage assessment and adjustment methodology for measuring the level of undercount in the 2011 Census.
The 2011 Census population estimates have been through a rigorous quality assurance (QA) process to ensure that users of census data have confidence in the quality and accuracy of the information.
2011 Census questionnaire processing involved data capture, scanning, envelope slitting, sorting, removing spines from questionnaires and shredding.
Capturing the data and estimating the population
The 2011 Census adopted a similar processing strategy to that used in the 2001 Census.
The 2011 Census questionnaires were designed to be electronically scanned to capture all the ticked responses and hold written answers in digital form. Once information from the questionnaires had been electronically captured in a database, the paper documents were pulped and recycled. The digital images will be held electronically to be made available as public records after 100 years.
For the first time, questionnaires could be completed online. Data processing systems monitored the quality of the data and calculated adjustments in case of error or omission. They also adjusted for any shortfall in the number of people detected by the census follow-up survey.
The data from 2011 Census was processed more quickly than it was for the 2001 Census, allowing more time for the extensive quality assurance procedures.