For the 2011 Census, all households in England and Wales received a 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.
The Annual Population Survey is a continuous household survey. Most people are interviewed in person first, and later by telephone. The sample is formed partly from waves 1 and 5 of the Labour Force Survey (in which selected addresses are contacted every 3 months) and partly from boost cases that are in the sample for 4 waves, spread one year apart.
Participants are randomly selected from the Royal Mail Postcode address File (PAF). The NHS communal accommodation list is also used and (in the case of remote parts of Scotland) telephone directories. All eligible individuals found at the selected address may be interviewed. Individuals are included in the dataset for this analysis if they respond themselves or if a family member responds on their behalf. The complex survey design has been taken into account when calculating confidence intervals.
The achieved APS sample of approximately 275,000 undergoes weighting which is structured at local authority level and uses age and sex dimensions.
Weighting is used to adjust the results of a survey to make them representative of the population and improve their accuracy.
For example, a survey which contains 25% females and 75% males will not accurately reflect the views of the general population, which we know is around 50% male and 50% female.
Statisticians rebalance or ‘weight’ the survey results to more accurately represent the general population. This helps to make them more reliable.
Survey weights are usually applied to make sure the survey sample has broadly the same gender, age, ethnic and geographic make up as the general population.
The Office for National Statistics population estimates and projections are used as the basis for this weighting process.
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
All percentages are rounded to 1 decimal place.Quality and methodology information