TY  - JOUR
AU  - Glaeser,Edward L.
AU  - Sunstein,Cass R.
TI  - Extremism and Social Learning
JF  - National Bureau of Economic Research Working Paper Series
VL  - No. 13687
PY  - 2007
Y2  - December 2007
UR  - http://www.nber.org/papers/w13687
L1  - http://www.nber.org/papers/w13687.pdf
N1  - Author contact info:
Edward L. Glaeser
Department of Economics
315A Littauer Center
Harvard University
Cambridge, MA 02138
Tel: 617/495-0575
Fax: 617/495-7730
E-Mail: eglaeser@harvard.edu

Cass Sunstein
Law School
University of Chicago
1111 E. 60th St.
Chicago, IL 60637
E-Mail: cass_sunstein@law.uchicago.edu
AB  - 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 where there are 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.  We discuss the implications of Credulous Bayesianism for law and politics, including media policy and cognitive diversity on administrative agencies and courts.
ER  -