Protesters rally against government tax and spending policies at the U.S. Capitol on September 12, 2009, in Washington, D.C. (Photo: Rena Schild/Shutterstock)

With over 1.7 million viewers each evening, Fox News has the largest viewership of any cable news network. It is also one of the most trusted sources of political information.

In 2006, the Congressional Cooperative Elections Survey asked 15,000 Americans which of seven major news providers they thought provided the fairest coverage of national news. Almost 38 percent chose Fox News, and no other network came close. PBS ranked second, but only 18 percent of Americans said that it provided the fairest coverage.

Divide these results by the party identification of the respondent and we see a decidedly polarized result. Less than four percent of Democrats and 30 percent of Independents thought Fox News was the most fair, but over 77 percent of Republicans did. No other network has such a strong following of supporters.

It’s well documented that Fox News has a conservative bent. For example, Tim Groseclose and Jeffrey Milyo conducted a study that tracked how many times news outlets referred to different think tanks and policy groups. The results showed that Fox News was more likely to cite and highlight right-leaning groups in its coverage. In fact, its coverage was to the right of most Republican members of Congress. Professor Tim Groeling found in another study that during the late 1990s Fox News was disproportionately likely to report polls that showed a decrease in public approval for President Bill Clinton, and the Pew Research Center study found that in the final months of the 2008 campaign, only six percent of Fox News coverage of President Obama was positive, while 46 percent was negative. Other research has also found that when covering the topic of climate change, Fox News is more likely to interview people who dismiss climate change theories than climate change supporters.

To be sure, it is nothing new for media outlets to have a partisan slant: In the 18th and 19th centuries, newspapers were usually open about their partisan and ideological proclivities. But until now, the scholarship on the results of the ideological coverage on television has been inconclusive. It’s never been clear if media is just playing to the demands of their viewership or if the partisan slant of news coverage has electoral and institutional consequences. However, the gradual rollout of Fox News over a period of many years has given scholars a unique way to test if ideological media coverage actually has political consequences.

In March of 1996, Rupert Murdoch announced the introduction of the Fox News network. But the introduction of Fox News did not happen nationally. Instead it was available in only a limited number of cable markets in 1996 and expanded slowly and steadily over the years. In one estimate, even by 2000, only a third of the population had access to a cable carrier that carried Fox News. It is a unique natural experiment because some Americans had access to Fox News, while others did not. Importantly, the places that received Fox News were not more conservative than the places that did not; which towns had access to Fox News first and which did not was largely idiosyncratic. This circumstance has allowed social scientists to test the effect that Fox News has had on voters and elected representatives.

Professors Daniel Hopkins and Jonathan Ladd found evidence that exposure to Fox News primarily increased the likelihood that Republicans and Independents would vote for a Republican candidate.

Professors Stephano DellaVigna and Ethan Kaplan, using data on voters in over 9,000 towns, found that individuals from communities that had access to Fox News voted in larger numbers for George W. Bush in 2000 than did those in towns that did not offer Fox News. This implies a significant persuasion rate of voters and, quite importantly, the authors’ calculations suggest that Fox News may have shifted up to 10,757 votes in Florida toward Bush. Given that this is much larger than Bush’s official margin of victory of 537 votes in Florida, the authors argue that “while the entry of Fox News had a relatively small impact on the 2000 election, it may still have contributed to the Bush victory in the unusually close election.” Interestingly, they find a similar result for Senate races, which implies that the ideological effect of watching Fox extends even to races that the network did not cover in depth.

Using the same methodological approach of harnessing the “natural experiment,” professors Daniel Hopkins and Jonathan Ladd found evidence that exposure to Fox News primarily increased the likelihood that Republicans and Independents would vote for a Republican candidate. This finding is supported by other research that shows that information is less effective at changing people’s minds than reinforcing and encouraging more extreme versions of pre-existing beliefs. These results are critical because they indicate that the introduction of Fox News, MSNBC, and other partisan news may be a driving force behind the escalation in political polarization.

The natural experiment provided by the Fox News rollout has also allowed researchers to investigate what effect Fox News’ introduction has had on the behavior of elected officials. In a forthcoming article in the Journal of Politics, professors Joshua D. Clinton and Ted Enamorado found that representatives in districts where Fox News started broadcasting became less supportive of President Clinton than representatives in districts that did not have access to Fox News. And professor Kevin Arceneaux and his colleagues find that both Republican and Democratic members of Congress in districts in which Fox News was available voted more conservatively close to election time, a finding they attribute to the strategic considerations of elected officials. “As elections approach,” they explain, “members shift their attention to the subset of their district’s voters that they anticipate will turn out on Election Day. Here, the media composition of the district plays a particularly pronounced role. Members with Fox News in their district behave as if they believe that more Republicans will turn out at the polls.”

The critical takeaway that emerges from these studies is that the rise in ideologically slanted media has a real and measurable impact on American politics. Fox News has shaped and continues to shape American politics in dramatic ways, not least of which is the fostering of a more conservative and polarized electorate and Congress.

But perhaps a more important lesson is that the destruction of the Fairness Doctrine, which required broadcasters to cover issues of public importance and, importantly, to offer contrasting viewpoints of those issues, has had a measurable and negative effect on democracy in the United States.