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The Impact of the COVID-19 Outbreak on the Weak-Form Informational Efficiency of the Warsaw Stock Exchange (Wplyw wybuchu epidemii COVID-19 na efektywnosc informacyjna Gieldy Papierow Wartosciowych w Warszawie w formie slabej)

Author

Listed:
  • Jacek Karasinski

    (Faculty of Management, University of Warsaw, Poland)

Abstract

The aim of this paper is to verify whether the COVID-19 outbreak negatively affected the weak-form informational efficiency of the Warsaw Stock Exchange (WSE). Applying a wild bootstrapped automatic variance ratio test and the rolling window methodology, we verify the martingale hypothesis for daily returns of 437 stocks listed on the Main Market of the WSE i n a research period beginning on January 2nd, 2015 and ending on August 31st, 2020. The percentage of cases in which the martingale hypothesis cannot be rejected is our proxy for the weak-form informational efficiency that we come up with. Despite the rapid and significant price movements, as well as the rise of returns volatility (and thus a likely herd behavior of the market participants), the results obtained do not allow for stating unambiguously that the COVID-19 outbreak negatively affected the weak-form informational efficiency of the WSE. The results turned out to be sector-dependent. Future issue-related studies can apply other proxies of efficiency levels as a unique proxy applied in this study is based only on a wild bootstrapped automatic variance ratio test. The issue-related studies should be also continued as the pandemic is still an ongoing issue. This study comes up with a novel approach to approximating the weak-form informational efficiency, provides regulators, as well as other market participants with valuable information on the WSE efficiency changes in the COVID-19 pandemic times and even its long-term trends.

Suggested Citation

  • Jacek Karasinski, 2022. "The Impact of the COVID-19 Outbreak on the Weak-Form Informational Efficiency of the Warsaw Stock Exchange (Wplyw wybuchu epidemii COVID-19 na efektywnosc informacyjna Gieldy Papierow Wartosciowych w ," Research Reports, University of Warsaw, Faculty of Management, vol. 2(37), pages 15-28.
    • Handle: RePEc:sgm:resrep:v:2:i:37:y:2022:p:15-28
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    More about this item

    Keywords

    COVID-19; stock market; efficient market hypothesis; weak-form efficiency; martingale hypothesis;
    All these keywords.

    JEL classification:

    • G10 - Financial Economics - - General Financial Markets - - - General (includes Measurement and Data)
    • G14 - Financial Economics - - General Financial Markets - - - Information and Market Efficiency; Event Studies; Insider Trading
    • G17 - Financial Economics - - General Financial Markets - - - Financial Forecasting and Simulation
    • G40 - Financial Economics - - Behavioral Finance - - - General
    • G41 - Financial Economics - - Behavioral Finance - - - Role and Effects of Psychological, Emotional, Social, and Cognitive Factors on Decision Making in Financial Markets

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