Biased assimilation, homophily, and the dynamics of polarization

Abstract

We study the issue of polarization in society through a model of opinion formation. We say an opinion formation process is polarizing if it results in increased divergence of opinions. Empirical studies have shown that homophily, i.e., greater interaction between like-minded individuals, results in polarization. However, we show that DeGroot's well-known model of opinion formation based on repeated averaging can never be polarizing, even if individuals are arbitrarily homophilous. We generalize DeGroot's model to account for a phenomenon well known in social psychology as biased assimilation: When presented with mixed or inconclusive evidence on a complex issue, individuals draw undue support for their initial position, thereby arriving at a more extreme opinion. We show that in a simple model of homophilous networks, our biased opinion formation process results in polarization if individuals are sufficiently biased. In other words, homophily alone, without biased assimilation, is not sufficient to polarize society. Quite interestingly, biased assimilation also provides a framework to analyze the polarizing effect of Internet-based recommender systems that show us personalized content.T he issue of polarization in society has been extensively studied and vigorously debated in the academic literature as well as the popular press over the last few decades. In particular, are we as a society getting more polarized? If so, why, and how can we fix it? Different empirical studies arrive at different answers to this question depending on the context and the metric used to measure polarization.Evidence of polarization in politics has been found in the increasingly partisan voting patterns of the members of Congress (1, 2) and in the extreme policies adopted by candidates for political office (3). McCarty et al. (4) claim via rigorous analysis that America is polarized in terms of political attitudes and beliefs. Phenomena such as segregation in urban residential neighborhoods (5-7), the rising popularity of overtly partisan television news networks (8, 9), and the readership and linking patterns of blogs along partisan lines (10-13) can all be viewed as further evidence of polarization. On the other hand, it has also been argued on the basis of detailed surveys of public opinion that society as a whole is not polarized, even though the media and the politicians make it seem so (14, 15). We adopt the view that polarization is not a property of a state of society; instead it is a property of the dynamics through which individuals form opinions. We say that opinion formation dynamics are polarizing if they result in an increased divergence of opinions.It has been argued using empirical studies that homophily, i.e., greater interaction between like-minded individuals, results in polarization (12,16,17). This argument has been used to claim that the rise of cable news, talk radio, and the Internet has contributed to polarization: the increased diversity of information sources coupled with the increased ability to narrowly ta...

Beyond Social Contagion: Associative Diffusion and the Emergence of Cultural Variation

“…Carley 1991;Mark 1998;), whereas others focus on changes in the strength of social influence as a function of cultural similarity (e.g. Dandekar et al 2013;Flache and Macy 2011). 5 Whatever the differences in their underlying assumptions and emphases, all of these models describe a coevolutionary process whereby individuals become increasingly related to culturally similar others.…”

“…First, and drawing on existing literature (e.g. Friedkin and Johnsen 1990;Dandekar et al 2013), we assume that a social susceptibility parameter α, ranging from 0 to 1, determines the extent to which agents are susceptible to influence by others'…”

“…16 Experimental work demonstrates that this process pushes individuals toward extreme opinions, gradually leading to polarization (Lord, Ross, and Lepper 1979). We follow Dandekar et al (2013) and operationalize biased contagion as a function of a bias parameter β such that f ∼ V β Bi · V Ai (t) in eq. 8.…”

“…Following Dandekar et al (2013), we implement biased contagion as a function of B's prior preference for i, weighted by a bias parameter β > 0. β defines the extent to which B's existing preferences mediate social transmission from A. As long as β > 1, bias is positive.…”

“…These network diffusion models commonly attribute cultural heterogeneity to structural boundaries to diffusion. Studies either assume the preexistence of a segregated social structure whereby cultural practices diffuse within, but not across network clusters (Centola and Macy 2007;Dandekar, Goel, and Lee 2013), or that structural disconnection emerges endogenously through actors' tendencies or incentives to preferentially interact with others who are culturally similar (Axelrod 1997;Centola, González-Avella, Eguíluz, and San Miguel 2007;Mark 2003;Baldassarri and Bearman 2007). Whatever the underlying mechanism, the end result is a balkanized world in which people interact within culturally homogenous, and structurally separated cliques.…”