For Cass Sunstein, a challenge that social media poses to democracy was clarified by a social-science experiment that he conducted in two different communities in Colorado: left-leaning Boulder and right-leaning Colorado Springs. Residents in each place were gathered into small groups to discuss their views on controversial topics, like climate change and same-sex marriage. Afterward, they were asked to report on the opinions of their groups as well as their own views on the subjects.

The results were the same in both communities.

The effect of gathering into groups composed of mostly like-minded people to discuss controversial subjects was to make participants more set and extreme in their views:

(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. Before deliberation, the median view, among Boulder groups, was not always so far apart from the median view among Colorado City groups. After deliberation, the division increased significantly.

(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.

Sunstein, a Harvard faculty member, and Reid Hastie, a professor at the University of Chicago, wrote about their findings in “Wiser: Getting Beyond Groupthink to Make Groups Smarter.” And Sunstein returned to them Monday in a talk on social media and democracy at the Aspen Ideas Festival, which is co-hosted by The Aspen Institute and The Atlantic, where he ran through some of the explanations for group polarization.

Why does group polarization occur? There are three principal reasons, according to his research, which he once laid out at greater length in a Harvard Business Review article:

The first and most important involves informational signals—but with a few twists. Group members pay attention to the arguments made by other group members. Arguments in any group with an initial predisposition will inevitably be skewed in the direction of that predisposition. As a statistical matter, the arguments favoring the initial position will be more numerous than those pointing in another direction. Individuals will have thought or heard of some but not all the arguments that emerge from group deliberation. Thus deliberation will naturally lead people toward a more extreme point in line with what they initially believed.

The second reason involves reputation again. As we have seen, people want to be perceived favorably by other group members. Sometimes their publicly stated views are a function of how they want to present themselves. Once they hear what others believe, they will adjust their positions at least slightly in the direction of the dominant position in order to preserve their self-presentation.

The third reason stresses the close links among three factors: confidence, extremism, and corroboration by others. When people lack confidence, they tend to be moderate. The great American judge Learned Hand once said, “The spirit of liberty is the spirit which is not too sure that it is right.” As people gain confidence, they usually become more extreme in their beliefs, because a significant moderating factor—their own uncertainty about whether they are right—has been eliminated. The agreement of others tends to increase confidence and thus extremism.

There are Americans who wonder why this big, diverse country should try to stay together. Wouldn’t it be better, they argue, for cosmopolitan cities and coastal Blue States to go one way, while Red America goes another way, with both jurisdictions moving closer to the culture a majority of their members prefer?

On college campuses, too, there are those who wish that there was less diversity of viewpoint and belief, and seek to “train” everyone in the views that they regard to be settled and enlightened. And almost all of us belong to at least one social network where our feeds are disproportionately composed of content produced by people who are a lot like us.

But for all the benefits of agreement, solidarity, and spending time with like-minded people, there is compelling evidence of a big cost: the likeminded make us more confident that we know everything and more set and extreme in our views. And that makes groups of like-minded people more prone to groupthink, more vulnerable to fallacies, and less circumspect and moderate in irreversible decisions they make.

Conversely, if we can harness the strengths of viewpoint diversity, our collectives can reach better decisions. We can, in fact, be better off together than we would be apart.

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