We use the synthetic control method to analyze the effect of face masks on the spread of COVID-19 in Germany. Our identification approach exploits regional variation in the point in time when wearing of face masks became mandatory in public transport and shops. Depending on the region we consider, we find that face masks reduced the number of newly registered severe acute respiratory syndrome coronavirus 2 infections between 15% and 75% over a period of 20 days after their mandatory introduction. Assessing the credibility of the various estimates, we conclude that face masks reduce the daily growth rate of reported infections by around 47%.

中文翻译：

---

德国戴口罩大大减少了 COVID-19 病例 [统计]

我们使用综合控制方法来分析口罩对德国 COVID-19 传播的影响。我们的识别方法利用了公共交通和商店强制佩戴口罩的时间点的区域差异。根据我们考虑的地区，我们发现强制引入口罩后 20 天内，新登记的严重急性呼吸综合征冠状病毒 2 感染人数减少了 15% 至 75%。评估各种估计的可信度后，我们得出的结论是，佩戴口罩可将报告感染的每日增长率降低约 47%。