Political polarization and the electoral effects of media bias

Many political commentators diagnose an increasing polarization of the U.S. electorate into two opposing camps. However, in standard spatial voting models, changes in the political preference distribution are irrelevant as long as the position of the median voter does not change. We show that media bias provides a mechanism through which political polarization can affect electoral outcomes. In our model, media firms' profits depend on their audience rating. Maximizing profits may involve catering to a partisan audience by slanting the news. While voters are rational, understand the nature of the news suppression bias and update appropriately, important information is lost through bias, potentially resulting in inefficient electoral outcomes. We show that polarization increases the profitability of slanting news, thereby raising the likelihood of electoral mistakes. We also show that, if media are biased, then there are some news realizations such that the electorate appears more polarized to an outside observer, even if citizens' policy preferences do not change.