It is often claimed that international investment arbitration is marked by a revolving door: individuals act sequentially and even simultaneously as arbitrator, legal counsel, expert witness, or tribunal secretary. If this claim is correct, it has implications for our understanding of which individuals possess power and influence within this community; and ethical debates over conflicts of interests and transparency concerning ‘double hatting’—when individuals simultaneously perform different roles across cases. In this article, we offer the first comprehensive empirical analysis of the individuals that make up the entire investment arbitration community. Drawing on our database of 1039 investment arbitration cases (including ICSID annulments) and the relationships between the 3910 known individuals that form this community, we offer the first use of social network analysis to describe the full investment arbitration community and address key sociological and normative questions in the literature. Our results partly contradict recent empirical scholarship as we identify a different configuration of central ‘power brokers’. Moreover, the normative concerns with double hatting are partly substantiated. A select but significant group of individuals score highly and continually on our double hatting index.

It is often claimed that international investment arbitration is marked by a revolving door: individuals act sequentially and even simultaneously as arbitrator, legal counsel, expert witness, or tribunal secretary. If this claim is correct, it has implications for our understanding of which individuals possess power and influence within this community; and ethical debates over conflicts of interests and transparency concerning 'double hatting'-when individuals simultaneously perform different roles across cases. In this article, we offer the first comprehensive empirical analysis of the individuals that make up the entire investment arbitration community. Drawing on our database of 1039 investment arbitration cases (including ICSID annulments) and the relationships between the 3910 known individuals that form this community, we offer the first use of social network analysis to describe the full investment arbitration community and address key sociological and normative questions in the literature. Our results partly contradict recent empirical scholarship as we identify a different configuration of central 'power brokers'. Moreover, the normative concerns with double hatting are partly substantiated. A select but significant group of individuals score highly and continually on our double hatting index.

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The authorship of judicial opinions was an early target of computational legal studies (Oldfather et al., 2012). Principally focused on the US Supreme Court, different methods were deployed to identify the role of "unseen actors" in writing opinions. Motivated normatively by concerns about the disproportionate influence of clerks in "judicial ghostwriting" (Rosenthal and Yoon, 2011) and theoretically by an interest in the allocation and optimization of time in judicial labour (Choi and Gulati, 2005), research has sought to detect who are the authors of judgments, examine how they are influenced by unseen actors, and chart what variation exists across judges, actors and time.The methodology is grounded in stylometry, a linguistic theory premised on human authors leaving fingerprints in their writing and a method based on the statistical analysis of measurable patterns particular to literary style. Early stylometry focused on the prominence of "function words" (such as "a", "by", "if", "of" "their" and "who"), which were viewed as the most discernible textual fingerprint. The method permitted ground-breaking qualitative research in identifying authorship, among other things, of the Federalist Papers (Mosteller and Wallace, 1964), by focusing on the use of and placing of 63 function words. Others have sought to identify the authors of books of the Christian Bible (Morton and McLeman, 1966;Burns, 2006) and Shakespearean plays (Seletsky et al., 2007).This "supervised" approach to stylometry is backed by neurological studies, which show that preferences for function words develop late in children and that function and content words are stored and processed in different brain regions (Menn and Obler, 1990;King and Kutas, 1995). However, in stylometry theory, emphasis is also placed on features like word and sentence length, lexical frequencies, punctuation patterns, rare