In 2018, one of the major ESG data providers inverted the scale of its ESG ratings (along with making other changes to the data).
Since the scale was inverted, now minimum is the best score (0).
You can find a nice paper by Rzeźnik, Weiss Hanley, and Pelizzon (2021) on the topic:
“While the new methodology may correctly change investors’ perception of a firm’s ESG risk, the inversion of the scale makes inference about its meaning more difficult. Indeed, in some cases, investors appear to blindly implement a trading strategy based on the change in ratings without additional due diligence. We show that potentially incorrect assessments of the meaning of the change in ESG ratings shape investors’ portfolio allocation decisions and result in temporary price pressure on the affected stocks, even in situations where it is unlikely that new fundamental ESG information is conveyed by the ratings change.”
You can find the paper at: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3801703
