Take it with a pinch of salt-ESG rating of stocks and stock indices

This paper investigates the environmental, social, and governance (ESG) ratings of 20 leading stock exchange indices by analyzing and aggregating ratings of underlying stocks. ESG ratings are increasingly important inputs to sustainable investments in the European Union and United States with the phasing-in disclosure regulations. We find that ratings from two different rating providers (Sustainalytics and Refinitiv) for the same listed stocks are only weakly correlated, even if the scaling differences of the ratings are adjusted. Monte Carlo simulations are conducted to estimate how the choice of major ESG rating inputs (i) aggregation formula, (ii) weighting scheme and (iii) data provider influence the uncertainty of ratings and thus indirectly the sustainable investment process. The simulations reveal that the uncertainty is primarily related to choice of the ESG rating provider. We found that the popular best-in-class portfolio selection could be built on ESG scores. In lower segments of the ESG asset universe, investment selection becomes more challenging due to the increasing uncertainty of ratings. Finally, the paper shows that exchanges in the European Union provide relatively good ESG investment opportunities in international comparison.