A descriptive-exploratory analysis of assurance practices is presented in this paper, by analysing the patterns of sustainability assurance reporting in two national contexts with different levels of assurance activity (Italy and the U.S.) over a period of 11 years (2003/2013). The study is based on theoretical insights drawn from institutional sociology and normativity production. It is framed both in the Italian situation, where assurance statements consistently include a narrow set of formal and procedural communications, and in an unsettled situation in the U.S., where assurance activity is more incipient, but where experimentation in substantial assurance disclosure practices has more room to develop. Its main implication is that the diffusion of sustainability assurance and the creation of sustainability assurance disclosure norms are not without its cost: information quality does not increase with patterned practice. The results also point towards the noteworthy role of specific professionals in the earlier and later stages of assurance practice norms. They reveal a significant influence of non-Big4 firms (mainly certification bodies and consulting and engineering firms) in the diffusion of sustainability assurance disclosure norms. In contrast, the Big4 firms appear to be positively associated with the narrowing down of the assurance focus to a selected subset of this activity in later stages of the development of the assurance norm. In this regard, this study provides insight into the circumstantial—but relevant—carrier role of the Big4 firms in determining what “assurance” means.
