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Corona 2020: store closures had little effect, masks a big one
The study has been published on a preprint server, has undergone a peer review process and has already been accepted for publication. According to the study, the contact restrictions reduced the increase in coronavirus infections by almost 14 percentage points. This means that if there had been a 30% increase in cumulative infections in a region in a certain period of time without this measure, for example, infections actually only increased by around 16% thanks to social distancing and other contact restrictions. The obligation to wear masks in buses, trains, supermarkets and other public places also proved to be effective in flattening the curve and preventing the exponential spread of the disease: The obligation reduced the increase by a further 13.5 percentage points.
The closure of schools and daycare centers had a smaller but still significant impact of around 5.5 percentage points. Restaurant closures had an effect of around 2 percentage points, while the closure of parks, zoos, museums and wellness facilities - as well as stores - had a barely discernible effect. "The effect of store closures was barely detectable," states the head of the study, Kassel statistician Prof. Dr. Reinhold Kosfeld. One reason could be that there is usually much more space available in the closed stores than in the system-relevant stores that remained open, such as supermarkets.
Kosfeld continues: "Contact restrictions and compulsory masks were the pillars of success in containing the pandemic. The effect of closing schools and daycare centers was significant, but much smaller. The calculated effect accounts for 14 percent of the overall effect, i.e. around one seventh of the total success. The proportion drops to 6 percent for closures of restaurants, cafés and bars. The shutdown of non-essential retail is even lower at 4.5% and is no longer statistically reliable. It should be borne in mind that the effects are influenced by the chronology of closures during the crisis. Additional measures taken relatively late often have a smaller effect than the first measures."
Kosfeld also emphasizes that he calculated the statistical effect in the study, but does not make any statements on political reasons for certain measures, such as the closure and opening of educational institutions, nor does he describe any medical or epidemiological causalities. What's more, the measures were examined in spring 2020, when some framework conditions may have been different, such as the infection rate of the virus or the availability of rapid tests and vaccinations. "Nevertheless, it is worthwhile not just speculating about the effect of school, store and restaurant closures or their opening, but to draw on reliable experience from the first wave," appeals the statistician.
Kosfeld's research group used a so-called "difference-in-differences approach" for the analysis: they evaluated the data for 401 German districts and independent cities. As the measures were introduced at different times in the federal states, they were able to form groups of cities and districts in which the measures already applied and control groups in which they did not (yet) apply for certain periods of time. They also projected epidemic progression curves for each territorial unit using data from the RKI. They calculated that the districts and cities were in different phases of the pandemic, meaning that the rate of spread may have been higher in a Bavarian city than in a Mecklenburg district. The study period was mid-March to the end of April, when the first easing of restrictions came into force.
Kosfeld is an adjunct professor at the Institute of Economics at the University of Kassel. Until last fall, he was head of the Department of Statistics. In addition to the statistician from Kassel, scientists from the Universities of Mainz, Darmstadt and Southern Denmark were also involved. The study was published on the "Preprint Server for Health Sciences" medrxiv.org. It has been accepted for publication in the Special Issue "Covid-19 and the Regional Economy" in the Journal of Regional Science, one of the leading international regional science journals.
Link to the study on the preprint server (peer review process has now taken place): https://www.medrxiv.org/content/10.1101/2020.12.15.20248173v2
https://doi.org/10.1101/2020.12.15.20248173
https://www.hna.de/kassel/corona-universitaet-kassel-covid-studie-massnahmen-lockdown-90467982.html