CamdenNewJournal

The independent London newspaper

Don’t confuse mortality rate with case fatality rate

12 November, 2020

Covid-19: It is very important not to confuse ‘mortality rate’ which is the ratio of deaths to population, with ‘case fatality rate’ which is the ratio of deaths to cases 

• THE global mortality rate for Covid-19, at the time of writing, is at 1.28million which is less than 0.02 per cent of the global population, according to Johns Hopkins’s Worldometer.

By contrast estimates for the Spanish flu “put the death toll [mortality rate] at 50 million (about 3 per cent of the global population), and possibly as high as 100 million (more than 5 per cent)”. [Wikipedia and various sources].

It is very important not to confuse “mortality rate” which is the ratio of deaths to population, with “case fatality rate” which is the ratio of deaths to cases.

The problem with using the case fatality rate as an indicator of the severity of a disease – as our governments are now doing with Covid-19 – is that the results are variable depending upon the number of tests performed.

It is no surprise, then, that at the onset of the pandemic, misleading reports sent shock waves of alarm across the globe; such as the one from Biospace that inaccurately claimed “the fatality rate for the Spanish flu is calculated at about 2 per cent” and “the global fatality rate for Covid-19… is about 5 per cent”.

Because the media only seems interested in publishing the more frightening case fatality rates and not the empiric mortality rates for Covid-19, here is the mortality rate formula: “to calculate a death rate the number of deaths recorded is divided by the number of people in the population, and then multiplied by 100”. [Open University; epidemiology department].

CLARA WEISS,
NW3

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