An empirical assessment of assurance statements in sustainability reports: smoke screens or enlightening information?

- We examine current sustainability-related assurance practice.
- We analyse assurance statements through the lense of neo-institutional theory.
- We elaborate differences in assurance quality depending on different determinants.
- Isomorphism may diminish external and internal value of assurance statements.

In recent years, the number of companies using external third parties to assure their sustainability reports has increased. Previous studies have underlined the heterogeneous content of voluntary assurance statements and have attributed this to the fact that standards are vague and regulations are non-existent. Against this background, this study seeks to examine the quality of, as well as the similarities and differences between, assurance statements in sustainability reports. The paper specifically analyses content, applied standards, assurance engagements, and providers by applying content analysis to the assurance statements in non-financial reports. The results indicate differences in the content, executed processes, and concrete implementation of the standards. Non-accountants apply a wider diversity of methods, while assurance processes by accountants seem to be prone to isomorphism due to professionalisation, network effects, and uncertainty. The results are discussed in the context of isomorphism by templates and deinstitutionalisation and suggest that current practices may diminish the credibility, transparency, and internal benefits for management which could be otherwise derived from assurance statements.