Impact of Subprime and Covid-19 crises on WAEMU stock exchange efficiency: a classic Hurst vs dynamic Hurst approach

Financial markets are alternative sources of financing, above all, in the current context of financial globalization and the development of information and telecommunication technologies. In the WAEMU zone in particular, the size of the economies seemed insufficient to supply national markets without high costs. The union’s authorities therefore set up a regional market that seemed to be a beneficial outcome : the WAEMU stock market. This stock exchange has undergone significant modernizations since its inception, with the aim of achieving optimal resource allocation. The informational efficiency of this stock exchange has become a hot topic of interest among researchers and professionals, giving rise to a growing number of publications on the subject. Our article is set in this context and aims to analyze the WAEMU’s weak-form efficiency. Based on the limitations of traditional methods, we use new approaches. Firstly, the classic Hurst is a tool for characterizing market structure and analyzing efficiency. The results highlight the multifractal nature of the WAEMU’s market and the rejection of the null hypothesis of no memory in the return series. Given the resurgence of crises, it would be interesting to analyze stock market behavior during such events. We also study the impact of crises (subprime and covid-19) on efficiency, using the dynamic Hurst exponent to account for efficient market varying with time. The results show that during periods of crisis, the stock market alternates between efficiency and inefficiency. They also reveal that Covid-19’s impact was faster than subprime crisis. They also reveal that covid impact crisis was faster than that of subprimes. However, despite the big spike linked to the covid context, the composite index picked up and continued in the same vein.