Extremism and Social Learning

Extremism and Social Learning. By Edward L. Glaeser & Cass R. Sunstein
The Journal of Legal Analysis, Vol 1, No 1 (2009)

Abstract

When members of deliberating groups speak with one another, their predeliberation tendencies often become exacerbated as their views become more extreme. The resulting phenomenon—group polarization—has been observed in many settings, and it bears on the actions of juries, administrative tribunals, corporate boards, and other institutions. Polarization can result from rational Bayesian updating by group members, but in many contexts, this rational interpretation of polarization seems implausible. We argue that people are better seen as Credulous Bayesians, who insufficiently adjust for idiosyncratic features of particular environments and put excessive weight on the statements of others in situations of (1) common sources of information; (2) highly unrepresentative group membership; (3) statements that are made to obtain approval; and (4) statements that are designed to manipulate. Credulous Bayesianism can produce extremism and significant blunders—the folly of crowds. We discuss the implications of Credulous Bayesianism for law and politics, including media policy and cognitive diversity on administrative agencies and courts.

Introduction (excerpts):

Many people have celebrated the potential value of deliberation, including its uses in democracy (Habermas 1998), and it is tempting to think that group decision-making will both produce wiser decisions and average out individual extremism. In many settings and countries, however, researchers have found that group deliberation leads people to take more extreme positions (Brown 1986). The increased extremism, often called group polarization, is usually accompanied by greater confidence and significantly decreased internal diversity, even when individual opinions are given anonymously (Schkade, Sunstein & Kahneman 2000; Brown 1986, 207). These facts, which are summarized in Section 2 of this article, appear to cast doubt on the wisdom, and certainly the moderation, of crowds. If deliberation leads liberals to become more liberal, and conservatives to become more conservative, the effects of deliberation are unlikely to be desirable in both cases. Deliberation might account for the folly, not the wisdom, of crowds.

Group polarization has evident implications for many issues in law and politics. It suggests, for example, that like-minded jurors, judges, and administrative officials will move to extremes. If group members on a corporate board or in a political campaign are inclined to engage in risk-taking behavior, group deliberation will produce increased enthusiasm for taking risks. But the mechanisms behind group polarization remain inadequately understood, and it is difficult to make predictions or to offer prescriptions without identifying those mechanisms.

In Section 3 of this article, we show that group polarization is predicted by a highly rational process of Bayesian inference. If individuals have independent information, which is shared in the deliberative process, then Bayesian learning predicts that ex post opinions will be both more homogeneous within the group and more extreme than individual opinions. Bayesian inference suggests that individuals with access only to their own private information will recognize their ignorance and hew towards the center. The information of the crowd provides new data, which should lead people to be more confident and more extreme in their views. Because group members are listening to one another, it is no puzzle that their post-deliberation opinions are more extreme than their pre-deliberation opinions. The phenomenon of group polarization, on its own, does not imply that crowds are anything but wise; if individual deliberators tend to believe that the earth is round rather than flat, nothing is amiss if deliberation leads them to be firmer and more confident in that belief.