The puzzle of convex/concave ESG returns and large banks in MENA region countries

This study examines the linear and nonlinear impacts of the environmental, social, and governance (ESG) components on bank stock returns in the region of the Middle East and North Africa (MENA). It also investigates the impact of bank size on the nexus between ESG and bank stock returns. Using a sample of 59 banks from the 12 countries in the MENA region between 2010 and 2021 and applying generalized quantile regression, we find the following. Our results suggest that ESG components and bank stock returns have a nonlinear relationship. In other words, the link between the ESG components and stock market returns could be U-shaped, inverted U-shaped, or both. Additionally, we find that size influences the link between the ESG pillars and bank stock returns. With few exceptions, large banks strengthened the positive link between ESG components and stock returns. Our findings align with the concept of "too little of a good thing" or "too much of a good thing" effects, along with the law of diminishing marginal returns.