Statistical disclosure control
Before we publish census data, we go through processes to make sure individuals and households cannot be identified.
We call this process statistical disclosure control (SDC).
This process helps us make sure we are following the rules and laws that protect the confidentiality of census data.
Read more about the rules and laws that protect census confidentiality.
SDC involves controlling access to data and the level of detail that is available to census data users.
For Scotland’s Census 2022, we will use 3 main SDC methods:
- record swapping
- cell key perturbation
- flexible table builder rules
Record swapping
Record swapping means we will swap a small number of households with other demographically similar households in nearby areas.
For example:
We will swap household 1 in area A with household 2 in area B. In any published census outputs, the information from household 1 will be in area B and the information from household 2 in area A.
All households have a chance to be swapped. Those containing individuals with rare characteristics are much more likely to be selected for swapping.
Swaps are made between similar households to minimise the impact on data quality.
Swapping helps to ensure that people and households with rare characteristics cannot be identified in published outputs.
Record swapping was the main SDC method we used for Scotland’s Census 2011.
Cell key perturbation
An innovation for Scotland’s Census 2022 will be the availability of a flexible table builder tool. This will allow users to create their own tables from census data.
The table builder will use a method called cell key perturbation. This will help protect the confidentiality of data within tables.
When a user creates a table, small adjustments will be made automatically to cells in the table.
We outlined cell key perturbation in more detail at a stakeholder event in February 2020. You can download and read slides from this event in the Stakeholder events section on this page.
Flexible table builder rules
The flexible table builder will also have built-in rules to protect confidential information.
Any information that may identify an individual or household will not be available in the table builder tool.
For example, users will not be able to access tables containing very small cell counts at a geographic level.
UK harmonisation
We are working with the other UK censuses to make sure our SDC methods are harmonised, where appropriate.
We do this through a working group that we attend with the Office for National Statistics and the Northern Ireland Statistics and Research Agency.
Find out more about how we work with other UK censuses.
Stakeholder events
We have held 2 stakeholder events to explain our SDC plans in more detail.
In June 2017, we outlined our strategy for SDC to stakeholders, along with some early plans.
See the slides from the event.
In February 2020 we outlined our SDC methodology, as part of our broader statistical methodology approach.