Every day, now, we are seeing figures for ‘Covid deaths’. These numbers are often expressed on graphs showing an exponential rise. But care must be taken when reading (and reporting) these figures. Given the extraordinary response to the emergence of this virus, it’s vital to have a clear-eyed view of its progress and what the figures mean. The world of disease reporting has its own dynamics, ones that are worth understanding. How accurate, or comparable, are these figures comparing Covid-19 deaths in various countries?
We often see a ratio expressed: deaths, as a proportion of cases. The figure is taken as a sign of how lethal Covid-19 is, but the ratios vary wildly. In the US, 1.8 per cent (2,191 deaths in 124,686 confirmed cases), Italy 10.8 per cent, Spain 8.2 per cent, Germany 0.8 per cent, France 6.1 per cent, UK 6.0 per cent. A fifteen-fold difference in death rate for the same disease seems odd amongst such similar countries: all developed, all with good healthcare systems. All tackling the same disease.
You might think it would be easy to calculate death rates. Death is a stark and easy-to-measure end point. In my working life (I’m a retired pathology professor) I usually come across studies that express it comparably and as a ratio: the number of deaths in a given period of time in an area, divided by that area’s population. For example, 10 deaths per 1,000 population per year. So just three numbers:
- The population who have contracted the disease
- The number dying of disease
- The relevant time period
The trouble is that in the Covid-19 crisis each one of these numbers is unclear.
1. Why the figures for Covid-19 infections are a vast underestimate
Say there was a disease that always caused a large purple spot to appear in the middle of your forehead after two days – it would be easy to measure.