Please cite this article in press as: Matei, S. A., & Bruno, R.J. Pareto’s 80/20 law and social differentiation: A social entropy perspective. Public Relations Review (2014), http://dx.doi.org/10.1016/j.pubrev.2014.11.006 ARTICLE IN PRESS G Model PUBREL-1341; No. of Pages 9 Public Relations Review xxx (2014) xxx–xxx Contents lists available at ScienceDirect Public Relations Review Pareto’s 80/20 law and social differentiation: A social entropy perspective Sorin Adam Matei a,∗ , Robert J. Bruno b a Brian Lamb School of Communication, Purdue University, 100 N. University Drive, West Lafayette, IN 47907, United States b Communication Studies Department, City University of New York-LaGuardia, 31-10 Thomson Ave., Long Island City, NY 11101, United States a r t i c l e i n f o Article history: Received 19 August 2014 Received in revised form 14 November 2014 Accepted 17 November 2014 Keywords: Social media Social structure Online interaction Entropy Structural differentiation a b s t r a c t Unequal contributions to social media, whereby a vast amount of content is produced by a limited number of users, need a better, theoretically grounded explanation. The present paper argues that contribution inequality on social media can be considered a symptom of social differentiation, which can be detected via social entropy. A conceptual foundation for this perspective is offered, supported by an empirical example. We use social entropy to detect the evolution of contribution inequality on Wikipedia over a period of 9 years. The paper also offers suggestions for using the conceptual framework for better understanding social media contribution structure and functional roles for practical applications. © 2014 Elsevier Inc. All rights reserved. 1. Introduction Inequality in content creation on social media is well documented (Kittur, Lee, & Kraut, 2009; Kumar, Novak, & Tompkins, 2006). Often, only a tiny proportion of users is responsible for most of the content produced (Shirky, 2004, 2008). The phenomenon is usually assigned as a particular manifestation of Pareto’s 80/20 law: 80% of everything is caused/explained by 20% of the actor/units involved in the process. The skewed nature of the online collaborative process is a reason for concern (Palloff & Pratt, 2010), since it violates many expectations about the leveling effect of communication technologies (Tapscott & Williams, 2006). Yet, this inequality does not lead to the demise of the online production systems by discouraging low level contributors, as some expect. It might, in fact, play a positive role. Inequality in contributions typically betrays the presence of a leading group that is deeply invested in the fate of the online project or platform. Leadership groups ensure project continuity, motivate other users by example, and create shortcuts in the communication process (Preece & Shneiderman, 2009). Leaders induct new members in the ranks of productive users, teaching them how to behave in the new environment, how to perform simple or complex tasks, and coaching them for higher level roles. Furthermore, collaboration between leaders and the rest of the users creates a desire to excel, which may improve the quality of the knowledge produced by the group as a whole (Arazy & Nov, 2010). In what follows we will provide some insights into why and how inequality emerges and how it matters. We will discuss some examples, especially culled from Wikipedia and I will discuss how the lessons learned in that context can be applied to communication research in general and to public relations in particular. Choosing Wikipedia is justified by the fact that ∗ Corresponding author. Tel.: +1 317 416 5807. E-mail addresses: smatei@purdue.edu (S.A. Matei), rbruno@lagcc.cuny.edu (R.J. Bruno). http://dx.doi.org/10.1016/j.pubrev.2014.11.006 0363-8111/© 2014 Elsevier Inc. All rights reserved.