Do investors value the voluntary assurance of sustainability information? Evidence from the Spanish stock market

This study examines in the Spanish setting whether, after the passing of the European Directive 2014/95/UE, investors value positively the voluntary assurance of sustainability reports corresponding to the period 2014-2017 for a sample of listed companies. It also analyzes the valuation by investors of a series of assurance characteristics such as its quality, level of application (reasonable/high vs. moderate/limited), scope (complete vs. partial), and the type of assurance provider (accounting vs. non-accounting firms). Our results find that investors reward firms that adopt external sustainability assurance. Furthermore, we document that investors value to a greater extent those assurance statements with a broader scope, a high/reasonable level of assurance, and with a better quality. Our results are relevant for companies, investors, regulators, and practitioners, and justify the pertinence of the recent Law 11/2018 that places Spain as a European reference by requiring a mandatory assurance of sustainability information in order to increase its reliability and comparability.