Every day we see figures for number of COVID-19 deaths in the UK quoted in the media, but what do these mean, and which figures should we pay most attention to?
With the rising death rate, and the complexity and potential confusion surrounding this seemingly straightforward measure of the impact of COVID-19, we are increasingly being asked our view on which data should be regarded as the best measure of COVID-19 deaths.
Of course, whichever way the numbers are presented, each individual death is a sad event. But it is really important to understand the strengths and limitations of the data being considered in order to understand the pandemic and learn from what the UK has experienced.
There are many official sources of data and each has a place in helping understand the impact of COVID-19. Our blog from August goes in to more detail about the difference sources, their uses and limitations. Here we outline some of the key issues to consider when thinking about which figures to use.
What is the difference between figures by date of death and figures based on date reported? Which should I use?
A commonly used headline is the number of deaths reported each day in the UK Government’s coronavirus dashboard, based on deaths which occurred within 28 days of a positive COVID-19 test. This has the advantage of capturing all newly reported deaths each day. It is understandable that this figure makes headlines as it is the timeliest data published, and captures all the additional deaths (within 28 days of a positive COVID-19 test) which government has been made aware of within the previous 24 hour reporting period. However, it has limitations and it is really important that in the reporting of these figures the implications of these limitations are clear.
As well as data by date reported the UK government coronavirus dashboard includes data on deaths within 28 days of a positive COVID-19 test by date of death on the deaths page of the dashboard. These are usually considered to be reasonably complete from about five days after the reference date. Looking at data by date reported shows large fluctuations in numbers, particularly after weekends and bank holidays. Data on date of death will give a better sense of the development of the pandemic and the changing rate of deaths.
This difference between figures for date reported and date of death has been particularly notable in the period following Christmas and New Year given bank holidays and the higher rates of deaths seen over the period. For example, looking at data published on 21 January for deaths within 28 days of a positive COVID-19 test:
- Deaths by date of death have a current peak on 12 January with 1,117 deaths (compared with a peak of 1,073 on the 8 April).
- Deaths by date reported have a peak of 1,820 deaths on 20 January (compared with 1,224 on 21 April).
Data by date of death should always be used if possible.
How can I best understand if COVID-19 was the cause of death?
The data outlined on the coronavirus dashboard, highlighted above, are based on deaths within 28 days of a positive test. There will be occasions within these cases where an individual had a positive COVID-19 test, but this was unrelated to the subsequent death. There will also be cases where a death was due to COVID-19 but occurred more than 28 days after a positive test result. PHE has published information in a technical note which looks at the impact of the 28 day cut off compared with alternative measures.
A more reliable measure is based on data drawn directly from the system of death registrations and includes data where COVID-19 is mentioned on the death certificate. The Office for National Statistics (ONS) publishes weekly figures, including a UK figure drawing on data from National Records Scotland (NRS) and Northern Ireland Statistics and Research Agency (NISRA).
ONS data are based on information from death certificates and include cases where COVID-19 is likely to have contributed to death (either confirmed or suspected) in the opinion of the certifying doctor. The provisional count is published weekly, 11 days after the end of the time period it covers. These data have many strengths, but provisional figures first published will not capture all deaths due to registration delays.
How can I best understand the impact of the pandemic on deaths?
The measures outlined above all aim to give counts of deaths where COVID-19 infection was a factor in the death. A broader measure which looks at the change in deaths because of the pandemic, whether or not due to a COVID-19 infection, is “excess deaths”. This is the difference between the number of deaths we would expect to have observed and the number of deaths we have seen. This is generally considered to be the best way to estimate the impact of a pandemic or other major event on the death rate.
ONS published a blog alongside its latest publication of excess deaths, which highlights the complexities in this measure. For example, a single figure of how many deaths there have been one year compared with a previous year may not be helpful, due to changes in the population. For this reason, in addition to providing the counts of total deaths, ONS produces estimates for excess deaths in a number of different ways. In its weekly statistics it compares numbers and rates to a five-year average, so that is comparing a similar period in terms of life expectancy, advances in healthcare, population size and shape. It also publishes Age Standardised Mortality Rates for England and Wales so that rates taking into account changes to the population size and structure can be compared.