Over at the University of Chicago faculty blog, Cass Sunstein reports on an experiment on the effects of deliberation on views:

Deliberation Day and Political Extremism

A few months ago, David Schkade, Reid Hastie, and I helped to organize a kind of Deliberation Day in Colorado. (The events were sponsored and funded by ABC News, which should be broadcasting our experiment soon, in connection with a general discussion of political polarization in America.) Two cities were chosen: Boulder (a predominantly liberal area) and Colorado Springs (generally Bush country). About 60 citizens were brought together to explore three of the most controversial issues of the day: affirmative action, an international treaty to control global warming, and civil unions for same-sex couples.

People in Boulder deliberated with others from Boulder, and people from Colorado Springs deliberated with people from Colorado Springs. Thus people were generally sorted into groups of like-minded people. . . .

Our key question was this: What would be the effect of deliberation on people's views?

Here are our three major findings.

(1) Liberals, in Boulder, became distinctly more liberal on all three issues. Conservatives, in Colorado Springs, become distinctly more conservative on all three issues. The result of deliberation was to produce extremism — even though deliberation consisted of a brief (15 minute) exchange of facts and opinions! . . .

(2) The division between liberals and conservatives became much more pronounced. . . .

(3) Deliberation much decreased diversity among liberals; it also much decreased diversity among conservatives. After deliberation, members of nearly all groups showed, in their post-deliberation statements, far more uniformity than they did before deliberation.