The Impact of the COVID-19 Outbreak on the Weak-Form Informational Efficiency of the Warsaw Stock Exchange

• Authors: Jacek Karasiński

Title variants

PL

Wpływ wybuchu epidemii COVID-19 na efektywność informacyjną Giełdy Papierów Wartościowych w Warszawie w formie słabej

Abstracts

PL

Celem artykułu jest sprawdzenie czy wybuch epidemii COVID-19 negatywnie wpłynął na efektywność informacyjną Giełdy Papierów Wartościowych w Warszawie (GPW) w formie słabej. Za pomocą automatycznego testu wskaźnika ilorazu wariancji wykorzystującego procedurę niestabilnego bootstrapa oraz wykorzystując metodykę postępujących okien weryfikowana jest hipoteza martyngałowa dla dziennych stóp zwrotu 437 akcji notowanych na Głównym Rynku GPW w okresie badawczym rozpoczynającym się 2 stycznia 2015 r. i kończącym się 31 sierpnia 2020 roku. Odsetek przypadków, w których hipoteza martyngałowa nie może być odrzucona stanowi zaproponowaną w niniejszym badaniu miarę efektywności informacyjnej rynku w formie słabej. Pomimo znaczących i nagłych zmian cen na rynku oraz wzrostu zmienności stóp zwrotu (i stąd prawdopodobnych zachowań stadnych uczestników rynku), otrzymane wyniki nie pozwalają na wysunięcie jednoznacznego wniosku mówiącego, że wybuch epidemii COVID-19 negatywnie wpłynął na efektywność informacyjną GPW w formie słabej. Zachowanie efektywności po wybuchu epidemii różniło się między sektorami. Kolejne, ściśle powiązane badania mogą wykorzystywać inne miary efektywności, ponieważ unikalna miara zastosowana w niniejszym badaniu jest oparta jedynie na automatycznym teście wskaźnika ilorazu wariancji wykorzystującym procedurę niestabilnego bootstrapa. Badania powinny być również kontynuowane z uwagi na to, że pandemia jest ciągle trwającym zjawiskiem. Niniejsze badanie proponuje nowe podejście do szacowania efektywności informacyjnej rynku w formie słabej. Ponadto dostarcza regulatorom i innym uczestnikom rynku cennych informacji dotyczących zmian efektywności GPW w czasach pandemii COVID-19 oraz jej długoterminowych trendów.

EN

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.

Keywords

EN

COVID-19; stock market; efficient market hypothesis; weak-form efficiency; martingale hypothesis

PL

COVID-19; rynek akcji; hipoteza rynku efektywnego; hipoteza w formie; słabej; hipoteza martyngałowa

• Publisher: Uniwersytet Warszawski. Wydawnictwo Naukowe Wydziału Zarządzania
• Journal: Studia i Materiały
• Year: 2022
• Issue: 2(37)
• Pages: 15-28

Dates

published

2022

Contributors

author

Jacek Karasiński

• https://orcid.org/0000000343265044

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Identifiers

DOI

10.7172/1733-9758.2022.37.2

Biblioteka Nauki

21492269