COVID-19 numbers

In a time like this, there is much uncertainty. It may be the first time that the world is experiencing such a pandemic, but similar situations have been encountered before. People have lots of questions and they are looking for information. Unfortunately, there is a lot of misleading information available. It seems that most people don’t check such information. They just believe what they read. It is for this reason tragic when “official” websites provide misleading information.

One example is the incorrect representations of numerical quantities about the COVID-19 pandemic. Two such quantities that is for obvious reasons quite important for people is the recovery rate and the mortality rate. They give an estimate, based on the currently available statistics, of the chances for a person to recover or die from COVID-19, given that the person has contracted the decease.

The statistics, which is generally available (see for example Wikipedia), consist of three numbers provided for every country on a daily basis. These number are: the number of confirmed cases (CC), the number of deaths (D) and the number of recoveries (R). For example, on 14 June 2020, the quoted number for the whole world are:

CC = 7 763 921
D = 429 632
R = 3 682 950

From these numbers, one can now compute the mortality rate and the recovery rate. The mistake that one often finds is that these rates are computed by dividing D or R by CC. That gives a misleading result, because CC also contains the currently active cases that does not form part of D or R yet.

The correct way to compute the mortality rate is to divide D by the sum of D and R and multiply the result by 100 to express it as a percentage. In a similar way, the recovery rate is obtained to dividing R by the sum of D and R and then multiply it by 100. You will note that when you add up the mortality rate and the recovery rate you get 100%. That makes sense, because one would either die or recover. There is no other option.

Applying these calculations to the above statistics for the world, we find the mortality rate to be just over 10% and the recovery rate just under 90%. These rates differ from country to country. For instance, the current morality rate in the USA is about 15%, while for SA it is only 3.7%.

Why is it different for the different countries? This is an important question, because it affects people’s behavior. There are many possible reasons, including the age demographic of a country and the availability of medical facilities in the country. The mortality rates for different age groups are different: it increases for older people. If the number of active cases becomes too high, there may not be enough hospital beds and equipment to treat all those that need treatment. As a result, one can expect the morality rate to increase.

The government of a country needs to try and keep the number of active cases low enough so that those that need to treatment can get it. For that reason, they impose restrictions that are aimed to reduce the rate at which the virus is spreading. Restrictions may seem to be a violation of people’s freedom, but in this case it is necessary. However, a government can only do so much. If the people decide to ignore the regulations imposed by the government, because they want to exercise their freedom, then the virus would spread too fast, with the result that the number of active cases can increase above the level where the country would have enough medical facilities.

There are more numbers that are important, for instance the growth rate in the number of confirmed cases. That is a topic for another day.

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