# Facts and figures

„Mathematics satisfies the mind through its extraordinary certainty.“Johannes Kepler (1571 – 1630), German Astronomer

## Of apples and pears

###### How do you actually add the two fractions 1/24 (04/03/2020)and 713/12.432 (14/11/2020)?

Even if your last maths course was a little while ago, you instinctively know that the result cannot be 714/12,456. It is relatively likely that you will do it the way you once learned in your maths course. You will first create a common denominator by multiplication in order to then be able to add the numerators together.

The two fractions above represent the number of people testing positive for Covid-19 on 04/03/2020 and the number of Corona positives on 14/11/2020 in relation to the tests performed. You may detect a subtlety in this sentence. In the 04/03/2020 figures, we use the name of the disease Covid-19 caused by the Corona virus because ONLY symptomatic people were tested for the Corona virus during that time, not – as has been the case since the summer and so was the case in November – a mixture of symptomatic and asymptomatic people, i.e. those who present for testing merely because they have been invited for Large Scale Testing. Therefore, in November’s figures, we simply use the term Corona positive for those people who have somehow encountered the virus but have not necessarily contracted Covid-19. You realise that even if you were to create a common denominator numerically, you are still currently adding up two different groups, which can very easily contribute to a distorted perception of the pandemic.

Since the corona-positive and/or those suffering from Covid-19 are statistically recorded:

- the numbers in the numerator are added up without taking into account the denominator (the number of tests taken), for which we would have received a insufficient note (in Luxembourgish: eng Datz) in the maths exam.
- In the numerator, those who only tested positive (i.e. also those who tested false positive) are not differentiated from those with the disease.

We have taken this as an opportunity to take a closer look at the data material provided and to reprocess it according to generally accepted mathematical and statistical basic rules and present it to you in the **Facts and Figures** section.

This article was written in German, whereas the French and English versions are translations. On the Luxembourg site we have published a duplicate from the German.