Corona data: Why the incidence can no longer be trusted on Mondays

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A now-familiar image: a test center employee holding a test sample

Photo: Tom Weller / dpa

The summer wave has begun, the number of new infections every day is increasing - Corona is back.

But of all things, what is probably the most frequently quoted metric of the pandemic sends ambiguous signals: the seven-day incidence is actually intended to describe how many people per 100,000 inhabitants had a corona infection detected by a PCR test within a week.

In the future, SPIEGEL will no longer devote its own report to the value on Sundays and Mondays.

Since its introduction, the corona incidence has shown methodological weaknesses.

The values ​​between the regions are only comparable to a limited extent.

In addition, the applicable test rules also affect how many infections are found at all.

Now another problem arises.

more on the subject

• Reporting gaps on the weekends: The creeping farewell to the daily corona numbersBy Patrick Stotz

• Analysis of the 7-day incidence: That's why the RKI numbers are often far too lowBy Holger Dambeck, Theresa Palm and Philipp Kollenbroich

• Live data on the corona virus: the most important figures for Germany by Marcel Pauly

• Data FAQ: The fine print on corona statisticsBy Marcel Pauly and Patrick Stotz

Every case report is recorded by the local health authorities, then sent to the responsible authority in the respective federal state and from there to the Robert Koch Institute (RKI).

For a few months, several federal states have refrained from forwarding data to the RKI at weekends.

Read more about the background here.

They are only transmitted on Mondays and taken into account in the data published by the RKI on Tuesdays.

Since the beginning of the month, the RKI has also refrained from reading in the reports received from the other federal states the day before on Sundays.

They only flow into the publication on Monday.

As a result, the seven-day incidences of the RKI on Sundays and Mondays are significantly too low.

They can make it appear as if the rate of infection is decreasing when the opposite is the case.

The SPIEGEL therefore refrains from picking up the value on Sundays and Mondays.

Because of the methodological problems, SPIEGEL has long focused on the absolute number of infection reports received by the RKI every day when describing the nationwide corona situation.

Averaged over seven days, this metric is significantly less susceptible to reporting-related fluctuations than the seven-day incidence.

Within a test regime, uptrends and downtrends are meaningful.

We proceed analogously with hospital admissions and deaths.

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