The Global Reporting Initiative (GRI) can be considered as one of the most extensively used model of sustainability reporting. The assurance statement (AS) is the mechanism to give trust to stakeholders about the accuracy of the information published in the sustainability reports (SRs) by the companies.
Please refer this paper for details as well as check GRI website for further learning
Measuring quality of sustainability reports and assurance statements: Characteristics of the high quality reporting companies
Article Measuring quality of sustainability reports and assurance st...