Mid-year population estimates from the Office for National Statistics (ONS) for England & Wales have arrived within Local Insight as both new denominators for various indicators across the site, as well as useful standalone indicators.
The mid-year estimates (MYE) aim to represent a population count as of the middle of the year (June 30th). The ONS generates these estimates by taking the most recent Census population snapshot as a starting point and then employs various data sources, such as births, deaths, and migration, to project population changes for subsequent years
Until now, MYE denominators for England and Wales used within the Local Insight platform have been based on the 2011 Census. These new mid-year estimates have been ‘rebased’ using the 2021 Census counts, covering 2021 and 2022, and will now be used as denominators for Local Insight indicators.
You can read more about how the ONS have done the rebasing in their blog post, and their analysis of this work.
There are 1874 indicators that are having their denominators updated in this change, 709 of these are being updated to use 2021 MYE denominators, and 1165 are being updated to use 2022 MYE denominators.
Later in the year, we expect to get 2023 MYE, as well as reworked versions of all mid-year estimates – back to 2011 – adjusted based on the Census 2021 results. These will all be added to Local Insight when they become available.
Population estimates for most local authorities have changed by around 5%, either positively or negatively, as a result of the rebasing of the ONS mid-year population estimates.
The rebased estimates for England and Wales also increase the female population and decrease the male population for all years. In Wales, however, the decreases to the population estimates for males was larger than those for estimates of females.
The shift to the newer MYE data as the denominator has now been implemented for the years 2021 and 2022 for England and Wales. For Scotland, just 2021 MYE data has been added. For indicators with numerators from 2022 or later, the 2022 denominators will be utilised.
For indicators that have been affected, you may see a few changes:
Another example of where there might be larger differences is in areas with a high Unattributable Population Change (UPC) – which is defined as a change to population estimates that can’t be explained by the ONS components of change. Large cities with a significant student population, like Coventry, are more likely to have high UPC – as are areas with a large proportion of young, mobile residents.This is because previous rounds of MYE spread the UPC evenly across all age groups. The new approach recognises that unexplained population changes are typically concentrated among certain age groups that are more transient, rather than being evenly distributed.As a result, areas with larger young adult populations are now seeing bigger adjustments in their population estimates compared to the previous method. The ONS explores this within their blog.MYE indicators have been added to England and Wales Local Insight within the following topics: 5-year bands from 0-5 up to 85-90+, total population, population density and broader grouping (for example 0-65 and 0-19).
For the full list of new indicators, download this spreadsheet. [Right click and ‘Save link as…’ to download]
These indicators are not assigned to a theme and will need to be added to a theme to be viewable on the map. For assistance in doing this, we recommend taking a look at the Help Centre article on adding new indicators to your themes. [Subscription only access]
These indicators can be viewed on the dashboard for all your custom areas: simply navigate to the dashboard, click Data and Custom Dashboard. You can then search [Subscription only access] for the indicators using their names.
Which population indicators do you recommend are used? The count from the 2021 Census, or these new mid-year estimates?
Whilst there are likely still situations where the Census 2021 population figures may be better suited, generally we would say that the Mid Year Estimates (MYE) are recommended for a more up-to-date picture of the population in your area.
To clarify, the MYE takes the census estimates as a starting point and rolls them forward based on information regarding births, deaths and administrative data on internal and international migration. This is also why we have made it a priority to implement them as denominators for various Local Insight indicators so shortly after their release. They are considered particularly reliable at Local Authority geography levels and above but be aware they are progressively less so for smaller areas.
Why are the 2021 Census population indicators still being used in Reports, and when will the MYE indicators be used?
This update has laid the groundwork for a second stage of MYE updates, where we intend to include the MYE in Reports. This will happen when the backdated MYE data becomes available (for 2011 to 2020) so that we can show how an area’s population is changing in time series charts. We will also update older MYE denominators with this data.
We expect this data to be made available over the next few months, as well as further Scottish MYE data, and 2023 data. At this point we will also replace the relevant Census 2021 population figures with the most recent MYE data – which we expect to be the 2023 MYE. These decisions have been made to strike the balance of giving Local Insight users new data as soon as possible but also to manage the staggered release of MYE data from the ONS in a consistent way across the site.
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