Modern Portfolio Theory associates the stock market risk with the volatility of return. Volatility is measured by the variance of the returns' distribution. However, the investment community does not accept this measure, since it weights equally deviations of the average returns, whereas most...

This paper analyzes market efficiency (EMH) with the day-of-the-week effect and the changes that might appear after the outbreak of the COVID-19 pandemic, based on the example of the OMX Exchange and its indices. Before the pandemic, only the OMX Baltic All-share index was efficient; during the...