The Basic Idea Behind Socially-Weighted Prevalence
The starting point was the observation that, especially in Italy, older people were overrepresented in the number of reported infections. We did not attribute this to the spread of the disease, but to the test procedure: especially when the health system reaches its limits, mainly people showing symptoms are tested. At the same time, we kept in mind that the severity could be age-related.
In a first step, we determined how many undetected infections should be in the different age groups so that at least the same rate occurs in all groups (called prevalence). We took the highest prevalence of the 90+ age group as a basis and extrapolated all other groups to this value.
We then argued that not all groups have the same number of social contacts. Children attend kindergartens and schools; adults go to work; pensioners are mainly in smaller private social groups. Based on the data from April 2, 2020, we determined a dark figure of 22,107 unrecognized infections for Germany. At that time, 73,000 infections were officially reported, resulting in a total of approximately 95,000 infections. This would mean that around 80% of infections are actually recognized in Germany. As teased above, there are updated figures at the end of the article. In the disclaimer above, we strongly recommend to really read the sections on the way there and not just to scroll to the end.