Lada Adamic: The news people read in Facebook supports their views
This may lead to a situation in which friends reinforce each other's opinions and people do not receive news that might challenge their own perspective.
Research done on the accounts of American Facebook users confirm this assumption. Users receive political news from less than one-third of the people who report having a political view that is clearly different from that of the user. A slightly smaller share of news items that are clicked open come from people who have a different political view than the user.
Watch Ademics talk here.