When is a death not a death?
On the 12th of August 2020, Public Health England announced a new definition of a Covid-19 death.
The original definition:
"A death in a person with a laboratory-confirmed positive COVID-19 test and either died within 60 days of the first specimen date or died more than 60 days after the first specimen date, only if COVID-19 is mentioned on the death certificate"
The new definition:
"A death in a person with a laboratory-confirmed positive COVID-19 test and died within (equal to or less than) 28 days of the first positive specimen date"
Adopting the new definition led to an overnight drop in the UK Covid-19 death toll of more than 5,000. Both definitions are non-specific and leave room for doubt — someone who had tested positive for Covid-19 but died from another cause is counted, while someone who may have died of Covid-19 but not been tested is not counted.
How do we determine how many deaths were truly "caused" by the virus? The most principled approach is a counterfactual one: imagine two parallel universes, one in which Covid-19 exists and one in which it does not. The difference in total deaths between the two universes gives us the number of deaths caused by the pandemic. Of course, we only observe one universe — ours — so we must estimate what would have happened without the virus.
The most sophisticated approach to this estimation involves esoteric mathematical modelling and statistics. The moral of the story: be very skeptical of interpreting widely reported death tolls as indicating the number of deaths caused by Covid-19.