COVID-19 has profoundly changed the way that we study and work. For students, especially primary and middle school students, online education has become a solution to learning problems. However, online and offline education have their own characteristics and different learning efficiencies in...

Does high-frequency trade increase or decrease volatility in financial markets during crises? We introduce a novel intraday volatility measure for ETFs, and find that during the COVID-19 crisis period, the withdrawal of high-frequency trade from large stock ETFs increases intraday ETF volatility...