COVID-19 pandemic and day-of-the-week anomaly in OMX markets

This paper aims to discuss market efficiency due to the changes that appeared in this field after the COVID-19 outburst. The OMX exchange and its indices are taken into consideration because they represent markets not analysed in such a context before (a) Baltic: Estonia, Latvia and Lithuania; (b) Scandinavian: Denmark, Finland, Iceland, Norway and Sweden). Two periods before and during the COVID-19 pandemic are considered (January 2009 to January 2020 and February 2020 to February 2021), and the efficient market hypothesis is tested together with the day-of-a-week effect anomaly to recognize the differences in market efficiency that could appear under special conditions, such as a pandemic. The results indicated that the impact of this pandemic on market efficiency was positive in most of the OMX markets studied. The added value of the article is related to supplementing the theory of market efficiency and showing that in difficult times investors make more rational decisions.