UK harmonisation

The Office for National Statistics (ONS) is responsible for planning and conducting Census 2021 in England and Wales.

Northern Ireland Statistics and Research Agency (NISRA) and National Records for Scotland (NRS) are responsible for Census 2021 in Northern Ireland and Census 2022 in Scotland respectively.

The Conduct of the 2021 and 2022 Censuses in the UK, published 28 January 2021, is the most recent statement of agreement between the National Statistician and the Registrars General for Scotland and Northern Ireland. The agreement aims to enhance the extent of harmonisation that takes place across the UK Censuses in 2021 and 2022.

This updated statement of agreement supersedes the previous version, The Conduct of the 2021 Censuses in the UK (PDF, 165 KB), that was published before the decision was made to move Scotland’s Census to 2022.

In collaboration with NRS and NISRA, we have published updates, against the original statement of agreement, outlining the progress made by the three census offices towards aspects of harmonisation:

• November 2020 update
• November 2019 update
• November 2016 update (PDF, 321 KB)

Any future updates on progress will be made against the new statement of agreement.

Following the decision to move Scotland’s Census to 2022, NRS, the ONS and NISRA are working closely to manage the dissemination of UK-wide census results where feasible. This includes increasing engagement with UK data users and exploring options for meeting their needs.

The UK censuses allow users – including government, local authorities, academics, commercial businesses and the general public – access to important information and statistics on the people and households of the UK. These data and statistics must be of high quality and of public value to meet the standards set out in the Code of Practice for Statistics.

First, we should harmonise to meet the principles set out in the statement of agreement between the National Statistician and Registrar Generals on The conduct of the 2021 and 2022 Censuses in the UK.

Second, responses to the Census 2021 Outputs and Dissemination consultation indicated all census outputs should be UK- harmonised where possible, in particular data definitions and outputs released.

Finally, we should comply with the Code of Practice for Statistics. In particular, the main practices are the trustworthiness pillar (that is, the Chief Statistician or Head of Profession for Statistics should encourage collaboration, harmonisation and innovation with other organisations, both inside and outside government, and across professional groups) and the quality pillar (that is, that the statistics, data and metadata ) should be compiled using recognised standards, classifications and definitions). They should be harmonised to be consistent and coherent with related statistics and data where possible.

Users should be provided with reasons for deviations from these standards and explanations of any related implications for use).

The censuses in all the UK constituent countries have been designed to be undertaken in a consistent manner. The three census offices are working closely with each other through multiple topic-based harmonisation working groups that aim to harmonise the approach to the 2021 and 2022 censuses where possible and to maximise the ability to produce UK-wide census information.

There are also specific working groups focusing on the harmonisation of census outputs specifically, as well as any engagement undertaken within topic areas.

There will be some necessary differences in a number of the questions asked, how data are processed, and some specific methodologies used. Information on these differences and the impacts that they have on comparability of data will be made available through the individual countries’ websites as work on the harmonisation of the 2021 and 2022 censuses continues.

Work is ongoing to share the lessons learned and best practice from each census office and to identify and explain any areas where UK harmonisation is not possible.

We aim to harmonise the following components of Census 2021 output content across the UK, where possible:

• questions
• definitions of concepts
• classifications
• output category content and labels
• output geographies

We are working collaboratively across the three census offices to ensure the census information provided by each UK constituent country is as harmonised as possible.

Our approach is to:

• prioritise the harmonisation of outputs
• ensure census statistical processes are harmonised where possible, for example, each statistical disclosure control methodology

We will produce documentation to support the Census 2021 outputs that will outline the approach taken to ensure harmonisation of questions and outputs. This documentation will also provide you with information to show where harmonised outputs have been produced.

More information about the 2011 UK censuses is available.

As part of the National Statistics accreditation for Census 2021, each of the three UK census offices publish reports that demonstrate compliance with the Code of Practice for Statistics, including aspects of harmonisation.

View all reports published to date on the following web pages:

• Office for National Statistics
• Northern Ireland Statistics and Research Agency
• National Records for Scotland

Scotland’s UK data and UK harmonisation page and Northern Ireland’s UK data and UK harmonisation page are also available.

A new User Working Group for UK Census 2021 and 2022 Data has been set up. The purpose of the group is to provide a forum for sharing information and feedback between the UK census offices and UK census data users.

The group will inform development of a dissemination approach that maximises the benefit that can be gained from providing UK census outputs. If you would like to register an interest in joining this group, or get involved in the development of the Census 2021 output content and design, please email Census Outputs team.

Our Census news page provides the latest updates on progress towards Census 2021. You can find out more about the design of the census, what we have done to develop the questions for 2021 and any upcoming events for Census 2021.