• The Korean Journal of Applied Statistics
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• v.33 no.5
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• pp.655-664
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• 2020

We apply the GSADF bubble test and its date-stamping method for the daily number of new COVID-19 cases. The test indicates statistically significant explosive expansions of the number of new cases whose periods of panic explosion are identified by the date-stamping method of the bubble test. The date-stamping analysis reveals that as of June 30 2020, the number of daily COVID-19 new cases are still explosively increasing for India; however, they stop explosively increasing (or are under control) for USA, Brazil, Russia, Spain, Turkey, China, and South Korea. It also reveals that South Korea has two disjoint periods of explosion: a stable period follows after the first explosion of 2020.02.20-2020.03.06, and then the second explosion occurs 2020.05.27-2020.06.01 with a stable period that continues up to 2020.06.30.