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Extremism and Social Learning

  • Edward L. Glaeser
  • Cass R. Sunstein

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.

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Paper provided by National Bureau of Economic Research, Inc in its series NBER Working Papers with number 13687.

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Date of creation: Dec 2007
Date of revision:
Publication status: published as Journal of Legal Analysis (Winter 2009) 1 (1): 263-324. doi: 10.4159/jla.v1i1.10
Handle: RePEc:nbr:nberwo:13687
Note: ED LE
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  1. Stephen Morris, 2001. "Political Correctness," Journal of Political Economy, University of Chicago Press, vol. 109(2), pages 231-265, April.
  2. Edward L. Glaeser & Bryce A. Ward, 2006. "Myths and Realities of American Political Geography," Journal of Economic Perspectives, American Economic Association, vol. 20(2), pages 119-144, Spring.
  3. Shleifer, Andrei & Mullainathan, Sendhil & Schwartzstein, Joshua, 2008. "Coarse Thinking and Persuasion," Scholarly Articles 11022284, Harvard University Department of Economics.
  4. Glaeser, Edward L. & Ward, Bryce A., 2006. "Myths and Realities of American Political Geography," Working Paper Series rwp06-007, Harvard University, John F. Kennedy School of Government.
  5. Edward L. Glaeser, 2004. "Psychology and the Market," NBER Working Papers 10203, National Bureau of Economic Research, Inc.
  6. Edward L. Glaeser & Bryce A. Ward, 2006. "Myths and Realities of American Political Geography," Harvard Institute of Economic Research Working Papers 2100, Harvard - Institute of Economic Research.
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