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As I live in Germany, I am trying to follow the local situation with attention.

The other day I saw a source (Financial Times) I was not following being shared on twitter, and I noticed that it was reporting significantly different numbers from what I am following (Die Zeit), hence this question.

In my search for an answer, I came across the plots from Ourworldindata, that I am adding to this question for comparison.


Source 1: Financial Times

Germany normalized new cases according to FT (click for larger version)

One can extract the following data points from this plot:

  • 190,9 new cases every 1.000.000 people on average for the week ending on November 2nd
  • 165,2 on November 3rd (a possibly incomplete number)

The Financial Times indicates the following as their source of the data:

Financial Times analysis of data from the European Centre for Disease Prevention and Control, the Covid Tracking Project, the UK Government coronavirus dashboard and the Spanish Ministry of Health. Data updated November 4 2020 11.58am GMT. Interactive version: ft.com/covid19


Source 2: Ourworldindata

Germany normalized new cases according to Ourworldindata (click for larger version)

One can extract the following data points from this plot:

  • 198,76 new cases every 1.000.000 people on average for the week ending on November 5th
  • 189,44 on November 3rd
  • 182,72 on November 2nd

The source is cited as:

Data published by European Centre for Disease Prevention and Control (ECDC) at https://www.ecdc.europa.eu/en/publications-data/download-todays-data-geographic-distribution-covid-19-cases-worldwide

The ECDC in turn gives the following source for Germany's data : https://experience.arcgis.com/experience/478220a4c454480e823b17327b2bf1d4 This page is titled:

Robert Koch-Institut: COVID-19-Dashboard
Auswertungen basierend auf den aus den Gesundheitsämtern gemäß IfSG übermittelten Meldedaten

i.e.:

Evaluations based on the reporting data transmitted from the health authorities in accordance with IfSG


Source 3: Die Zeit

Germany normalized new cases according to Die Zeit

One can extract the following data points from the website:

  • 140,8 new cases every 100.000 people on average for the week ending on November 5th
  • 136,4 on November 3rd
  • 132,7 on November 2nd

The sorce is cited as (translation in parenthesis in italics):

Quelle: Kreis- und Landesbehörden, RKI, eigene Berechnungen. (Source: District and state authorities, RKI, own calculations.)

And additional notes are provided for "bestätigteNeuinfektionen in den letzten 7 Tagen" (confirmed new infections in the last 7 days) and "bestätigteFälle seit Beginn der Pandemie" (confirmed cases since the pandemic began):

Die Anzahl der positiven Tests, die in den vergangenen sieben Tagen gemeldet wurden. Weitere Informationen unter der Infoschaltfläche »Bestätigte Fälle«.

Bei so vielen Menschen fiel ein Test auf das Virus Sars-CoV-2 positiv aus. Wer sich angesteckt hat, aber nicht getestet wurde, wird nicht gezählt. Da nicht jeder überhaupt Symptome verspürt und nicht jeder Verdachtsfall getestet wird, liegt die Dunkelziffer wahrscheinlich höher.

i.e.:

The number of positive tests reported in the past seven days. Further information under the information button »Confirmed cases«.

The number of people tested positive for the Sars-CoV-2 virus. Those who are infected but not tested are not counted. Since not everyone feels symptoms at all and not every suspected case is tested, the number of unreported cases is probably higher.


Now my question:

How is it possible that the same data (from RKI) leads to wildly different normalized numbers? Why does the FT and Ourworldindata report ~190 cases per million per week, while Die Zeit reports ~140 per 100.000 per week? Isn't that almost a factor x10?

Even accounting for delays in updating the charts and/or interpolations/extrapolations, I don't see how that is a reasonable difference.

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  • 3
    You have to be careful, there are different kinds of normalized numbers used for this. The one used in German media and politics is generally the total number of cases in a 7 days timeframe per 100,000 people. But also used is sometimes the number of cases per day averaged over 7 days per 1,000,000 people. – Mad Scientist Nov 5 '20 at 13:44
  • @MadScientist I see you're right. I did not notice the "daily" in the ourworldindata chart. would you mind answering so I can accept? – Federico Nov 5 '20 at 14:03
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As mentioned in a comment by Mad Scientist:

Ourworldindata reports around 200 cases per 1 million inhabitants per day where this number is the average over the last 7 days. DieZeit reports around 140 cases per 100.000 inhabitants in total over the last 7 days. With rounding these two incidence rates match up exactly.

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quarague's answer is exactly correct, I'm just spelling out the math so that it is obvious at a glance:

cases per day:
200 cases per 1 million inhabitants = 200/1000000 = 0.0002

140 cases per 100000 inhabitants, divided by 7 days = (140/100000)/7 = 0.0002

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