In Excess

The Economist is showing excess deaths by various countries. These graphs aim to track the effects of COVID-19. The New York Times has a similar publication. This article looks at excess mortality.

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The Economist uses a modelled ‘expected deaths’ line from EuroMOMO. (Image: The Economist)

Three measures

In the UK, there are three different sets of direct measures for COVID-19 deaths. These datasets have strengths and weaknesses.

DHSC & PHE

The Department for Health and Social Care collects new daily death records. Almost all these deaths are in hospitals, but refer to all four nations. Deaths are for people who have tested positive for the virus. The figures are when the records enter the system, not when the deaths occurred. This means we get weekly reporting cycles.

NHS England (Reconciled)

NHS England also provide daily updates of deaths in hospitals in England. The person who died must have tested positive for the virus. NHS England provide this data by both date of record and date of death. This is important for understanding when deaths have occurred.

ONS Death Registrations

The Office for National Statistics collects death certificates across England and wales. The count is for certificates which mention the virus. It does not need to result from a positive lab test. Doctors can mention the virus based on symptoms and clinical diagnosis.

There is a delay in publishing. Death certificates take time to register, process, and publish. Registrations are usually measured by date of registration. The ONS also publishes counts by date of death.

Excess Mortality

Excess deaths is the difference between deaths from all causes and a baseline value. That baseline is usually an average for previous years. For comparison, the ONS calculates the average weekly deaths between 2015 and 2019.

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This graph shows date of registration, not date of death. (Image: ONS)

In the week ending 10th April 2020 (week 15), there were 18,516 registered deaths. That is more 7,996 more deaths than the five-year average. There were 76% more registered deaths.

Excess mortality can be hard to interpret. These deaths are from all causes. Deaths may occur because of the virus, or because of the strain of healthcare systems. There may be other negative effects.

Why is excess mortality important?

Measuring excess mortality as the ‘total impact’ of an pandemic is not new.

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Excess mortality is a key measure. (Image: Joaquim Campa/Twitter)

Despite difficulties in interpretation, this measure has strengths:

  • Consistency: excess deaths are the number of deaths above a baseline. That means the same thing across countries and cities.
  • Reporting: the number of confirmed deaths depends on how many tests a country can do. A country may not test many people outside of hospitals. Doctors may show hesitance about recording clinical suspicions. Excess deaths are not influenced by these reporting practices.
  • Completeness: Pandemics put pressure on healthcare services. Without that pressure, a person’s illness may have been survivable. This is not a direct death from the virus. Some fatalities may not have happened during the pandemic.

As we study the impacts of COVID-19, excess mortality will be a key measure.

This blog looks at the use of statistics in Britain and beyond. It is written by RSS Statistical Ambassador and Chartered Statistician @anthonybmasters.

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