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Why do COVID-19 deaths in Sweden’s official data always appear to decrease?

Our World in Data presents the data and research to make progress against the world’s largest problems.
This blog post draws on data and research discussed in our entry on the Coronavirus pandemic.

There are two ways that COVID-19 deaths can be presented over time: by the date of death, or the date on which the death was reported. Neither of these methods is necessarily better than the other—but one should be aware of the difference as it can affect comparisons across countries and over time if these methods are not consistent.

The official data for deaths in Sweden is presented by date of death by Folkhälsomyndigheten, the Swedish Public Health Agency. This matters because it can take many days until all deaths for a particular day are reported in Sweden.

In practice this means that Sweden might today only report 10 deaths for yesterday, but once reporting is complete the death count for that same day might increase to 40.

The death counts for the last 2 weeks in Sweden should therefore always be interpreted as an incomplete count of what occurred in this period.

The mortality data presented by the Swedish Public Health Agency evolves over time

This undercount in recent days means that deaths often appear to be falling; but when this is later completed, data shows that more deaths were occurring during that period. This means that for the last 2 weeks of data, death counts in Sweden must only be interpreted as an incomplete measure of mortality.

As an example, this chart shows what confirmed deaths looked like for the period from October 20 to October 29, when the data was first published on October 30 (red series), and once many more death certificates had been added on November 12 (blue series).

One day after October 29, it looked as if deaths had peaked on October 27 and then started to fall, but in reality that’s not what happened over this period. What actually happened is shown by the blue series: deaths increased steadily.

This also means that each day, the Swedish government will add new deaths for multiple days in the past—mostly on recent days, sometimes for a longer period—if they have been reported with a long delay.

It is important to know these differences when studying the official data from Sweden, and even more when comparing it with other countries.

How confirmed deaths are presented in our data

Our source for COVID-19 cases and deaths, the COVID-19 Data Repository by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University, updates its figures for Sweden based on the date of report. More precisely, every morning Johns Hopkins University collects each country’s cumulative total number of cases and deaths since the start of the pandemic, and subtracts the previous day’s total from it.

This results in a daily figure that corresponds to the number of cases or deaths reported in the last 24 hours—regardless of when these deaths actually happened. This means that if the reported death toll for a country was 20 for a given day, it will remain 20 indefinitely.

Because the Swedish Public Health Agency doesn’t report on weekends and national holidays, the resulting series is more irregular, but it doesn’t show the same systematic fall for the last 2 weeks as the data presented by date of death, as for every other country.