Examining the efficiency of stock markets using multifractal detrended fluctuation analysis. Empirical evidence from OIC (Organization of Islamic Cooperation) countries during the GFC and COVID-19 pandemic

Purpose - This study aimed to examine the efficientmarket hypothesis (EMH) for the stockmarkets of 12 member countries of the Organization of Islamic Cooperation (OIC), such as Egypt, Indonesia, Jordan, Kuwait, Malaysia, Morocco, Pakistan, Saudi Arabia, Tunisia, Turkey and the United Arab Emirates (UAE), during the global financial crisis (GFC) and the COVID-19 (CV-19) epidemic. The objective was to classify the effects on individual indices. Design/methodology/approach - The study employed the multifractal detrended fluctuation analysis (MFDFA) on daily returns. After calculation and analysis, the data were then divided into two significant events: the GFC and the CV-19 pandemic. Additionally, the market deficiency measure (MDM) was utilized to assess and rank market efficiency. Findings - The findings indicate that the average returns series exhibited persistent and non-persistent patterns during the GFC and the CV-19 pandemic, respectively. The study employed MF-DFA to analyze the sequence of normal returns. The results suggest that the average returns series displayed persistent and non-persistent patterns during the GFC and the CV-19 pandemic, respectively. Furthermore, allmarkets demonstrated efficiency during the two crisis periods, with Turkey and Tunisia exhibiting the highest and deepest levels of efficiency, respectively. The multifractal properties were influenced by long-range correlations and fat-tailed distributions, with the latter being the primary contributor. Moreover, the impact of the fat-tailed distribution onmultifractality was found to be more pronounced for indices with lower market efficiency. In conclusion, this study categorizes indices with lowmarket efficiency during both crisis periods, which subsequently affect the distribution of assets among shareholders in the stock markets of OIC member countries. Practical implications - Multifractal patterns, especially the long memory property observed in stock markets, can assist investors in formulating profitable investment strategies. Additionally, this study will contribute to a better understanding of market trends during similar events should they occur in the future. Originality/value - This researchmarks the initial effort to assess the impact of theGFCandtheCV19pandemic on the efficiency of stock markets in OIC countries. This undertaking is of paramount importance due to the potential destabilizing and harmful effects of these events on global financial markets and societal well-being. Furthermore, to the best of the authors' knowledge, this study represents the first investigation utilizing theMFDFA method to analyze the primary stock markets of OIC countries, encompassing both the GFC and CV19 crises.