All households in England and Wales received a Census questionnaire through the post from the Office for National Statistics (ONS), along with an information leaflet and a pre-paid envelope for return by post.
Households in Wales received both English language and Welsh language questionnaires and information leaflets.
Householders could complete their questionnaire either:
- on paper, and return it by post
- online – each paper questionnaire had a unique internet access code
Responses were uploaded every day onto the questionnaire tracking system throughout the duration of the Census. This meant that households could be contacted if their questionnaire had not been submitted.
Communal establishments like care homes, and special groups (such as travellers), had their questionnaires hand delivered, collected and uploaded by Census employees. Individuals within communal establishments could also complete their questionnaire online.
There were 56 questions in the 2011 Census questionnaire:
- 14 questions were about the household and its accommodation
- 42 questions were for each member of the household
Topics included work, health, national identity, passports, ethnicity, education, second homes, language, religion and marital status.
There was an extra question about the Welsh language for households in Wales.
A census is designed to cover the whole population, but some people or households are inevitably left out by accident. A good census design will recognise this and take account of the error with quality controls.
ONS developed a ‘coverage assessment and adjustment methodology’ which estimates and adjusts Census data for the number of people and households not counted or counted incorrectly.
All the 2011 Census population estimates have been subject to quality assurance using demographic analysis, survey data, qualitative information and administrative data. This ensures that the figures are plausible and that users of Census data can have confidence in the quality and accuracy of the information.
Relative confidence intervals for the population by ethnicity down to local authority level can be found in the ONS archive.
Suppression rules and disclosure control
The ONS uses a number of ways to protect the confidentiality of individuals and households, including:
- record swapping, where small numbers of records are swapped between geographical areas
- restricting the amount of detail shown in published data, particularly at low level geographies like local authorities
Percentages are rounded to 1 decimal place.Quality and methodology information