Census 2001 results were the first to represent the entire population. This was achieved through a new strategy known as the 'One Number Census'(ONC). One of the key elements of the ONC was an independent follow-up survey. The Census Coverage Survey (CCS), as it is known, involved face to face interviews with a sample of 320,000 households from every local authority in the UK. In the past, the total population given by the census was the raw count, reflecting a response rate of 98 per cent. But by combining the results of the census and the CCS, it was possible in 2001 to estimate the total resident population - the 'one number' - to a high level of precision, plus or minus 0.2 per cent.
The One Number Census
Introduction to the One Number Census methodology.