COVID-19: impact of change to mid-year population estimates on case and death rates
An analysis of the impact to coronavirus reporting as a result of using updated population estimates from 2019 to 2020.
Applies to England
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Mid-year population estimates are produced annually by the Office for National Statistics (ONS). The 2020 mid-year population estimates (MYE) were published on 25 June 2021. The MYE contains estimates of both population and the components of population change (births, deaths and migration).
The 2019 mid-year population estimates are used in the UK Coronavirus (COVID-19) dashboard to calculate rates for cases and deaths at several geographical levels including UK, nation, region and upper and lower tier local authority.
Updating the MYE from 2019 to 2020 has an impact on the rates; the estimated number of people in an area forms the denominator of the calculation so a higher population will lead to a reduction in rate. The opposite is true for areas where the population has decreased.
UK and nations
The population of the UK at mid-year 2020 is estimated to be 67.1 million, an increase of about 284,000 (0.4%) since mid-year 2019.
While all 4 countries of the UK saw population increases in the year to mid-2020 there has been a divergence between the rates of population change. England and Wales grew at 0.47% and 0.53% respectively while Scotland and Northern Ireland grew more slowly (0.05% and 0.1% respectively).
Applying the 2020 population reduces the overall UK coronavirus case rate per 100,000 population from 7,906.2 to 7,872.7 (a reduction of 34 per 100,000 population). The UK coronavirus death rate is also reduced from 192.5 to 191.7 (a reduction of 0.8 per 100,000 population).
England regions
All regions in England show population growth between 2019 and 2020, ranging from 0.36% (North West) to 0.61% (East Midlands). This growth leads to a small reduction in coronavirus case and death rates in all regions.
Local authorities
It is estimated that the population increased in 294 out of the 374 local authorities of the UK in the year to mid-2020.
In England, just over 80% of upper tier local authorities show population growth between 2019 and 2020. However, most authorities (84%) show a small population change from 2019 to 2020, with a change of less than 1%. This means that the impact on coronavirus case and death rates is relatively small.
The local authority areas with the highest rates of population growth from mid-2019 to mid-2020 were predominantly areas of London such as Camden (3.5%) and Westminster (3.3%). In contrast, the areas that saw the greatest decrease in population were Lambeth (a decrease of 1.3%) and West Suffolk (a decrease of 1.0%).
The largest absolute change in coronavirus case rate is in Tower Hamlets, with a reduction of 222.8 per 100,000 population (from 10237.0 per 100,000 using 2019 MYEs to 10014.2 per 100,000 using 2020 MYEs). The largest absolute change in death rate is in Ribble Valley, with a reduction of 4.6 deaths per 100,000 population (from 248.0 per 100,000 using 2019 MYEs to 243.4 per 100,000 using 2020 MYEs).
Middle Super Output Area (MSOA)
Case rates by MSOA in England have been updated to use the latest population estimates for mid-2020, published by the Office for National Statistics. An analysis was conducted to determine the impact of this population change (from mid-2019 to mid-2020 populations).
Overall, the impact on coronavirus case rates at MSOA level is considered relatively small. In summary:
- the largest absolute change moving from 2019 to 2020 population estimates was for E02006843 (Cathedral and Kelham in Sheffield local authority): 2,333
- the largest percentage change moving from 2019 to 2020 population estimates was for E02000001 (City of London): 12.5%
- the population estimate for mid-2020 increased compared to mid-2019 for 3,829 MSOAs (56%), reduced for 2,917 MSOAs (43%) and stayed the same for 45 MSOAs (1%)
- the largest absolute 7-day case rate change moving from 2019 to 2020 population estimates was for E02005614 (Corby Village and Weldon in Corby local authority): -41.3 (from 806.9 to 765.6) per 100,000 population
- the median rate for MSOAs in England changed from 293.9 to 292.8 (-1.1) per 100,000 population
Note
The cumulative number of coronavirus cases and deaths stated above is as published on the UK Coronavirus dashboard on 15 July 2021. Rates by MSOA are for a 7-day rolling sum as published on 15 September.
Updates to this page
Published 5 August 2021Last updated 16 September 2021 + show all updates
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Added new analysis of the impact to coronavirus reporting of updated Middle Super Output Area (MSOA) population estimates (from 2019 to 2020).
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First published.