Release of local-level information involving small numbers carries a risk that individuals could be identified. We have carefully considered and assessed these risks, taking steps to reduce them as much as possible, and balancing them with the need to release useful information. We have been monitoring and reviewing our approach to how we release local-level information.
From 14 December 2020 we will be making changes to our approach. These changes have also been applied to the historic trend data, going back to March 2020. We will continue to monitor, assess and, where necessary, adapt our approach as the pandemic evolves further.
Summary of approach
We have summarised our approach. This covers where the approach has changed as well as where things remain as is.
The maps use local neighbourhood (Intermediate Zone) areas defined by the Scottish Government. Their geographical size varies because they are based on the number of people who live in the area. Most neighbourhood areas contain 2,500 to 6,000 residents, but some now have a notably lower or higher number. This is because their population has changed since these area boundaries were last reviewed.
We use population rates to colour the maps to show the number of confirmed cases in the context of the number of people living in that area. Users can view the number of cases in an information box that appears when they click on an area of interest. It is important to note that at this local level, population rates are sensitive to small changes in the number of cases. This means that areas with the same number of cases can be a different colour (a different population rate) because they have different population sizes. The rates associated with each colour are displayed on a scale above the map. We have adjusted this scale to take account of higher rates due to wider testing and the winter season. We have also changed the colour scheme to be clear that we are presenting the maps using a new scale.
Allocating cases to an area
Confirmed positive cases are now allocated to an area based on the postcode recorded in the testing system. Previously we allocated cases to local areas mainly based on their usual residential address recorded in the Community Health Index (CHI) database
Protecting patient confidentiality
Where a local neighbourhood has fewer than 3 positive cases, the actual number of cases and population rate has been suppressed (hidden) to help protect the identity of the individuals involved. This means that the number of cases is displayed as "0-2" and no population rate grouping is applied. These areas are coloured white on the maps. We previously grouped "1-4" cases to suppress very small numbers, but retained the rate grouping. In some instances, this allowed users to calculate small numbers by combining the rate category and population size. We monitored this and concluded that it was possible in an unacceptably high number of instances. Where a Local Authority has fewer than 5 positive cases in the selected 7 day period, a more detailed map will continue to be unavailable.
We regularly monitor user feedback and make small changes to improve labelling, notes and text on the dashboard. We have added a question and answer section underneath the map to respond to frequent questions we receive. The changes we have made make the information presented more meaningful by:
- widening the rate categories to reduce instances where very small differences in the number of cases result in big shifts in map colour
- suppressing (hiding) small numbers to reduce low-level noise where very high rates are driven by only 1 or 2 cases
- adding new categories to the higher end scale to make it easier to see local variation and changes over time in areas with higher rates
We are releasing open data files for neighbourhood (Intermediate Zone) level data. These files include historic trend data. They are refreshed daily to give the latest available figures and add any amendments to historic data that have been made. The same suppression approach is applied to these data. You can access the full suite of open data files on the Scottish Health and Social Care Open Data.