Matthew Levendusky is associate professor of political science at the University of Pennsylvania. He is the author of How Partisan Media Polarize America.

A generation ago, if ordinary Americans turned on the television at 6 p.m., they had basically one choice: to watch the evening news. They could have chosen to watch ABC, CBS, or NBC, but it wouldn’t really have mattered, because they all basically gave the same news in a similar format. Today, if they did that, they would have hundreds of options, including not just the news, but also sports, movies, re-runs, and so forth. Even within news, they have a variety of choices. Not only would they have the major network news programs, but they would have many choices on cable, most notably the partisan outlets of Fox News and MSNBC (not to mention even more choices online). This choice of explicitly partisan outlets means that individuals can choose to hear messages that reinforce their beliefs, while avoiding those from alternative points of view, which some claim leads to polarization. Does this high-choice media environment, especially with its partisan outlets, polarize the public?

The evidence suggests that the media may contribute to polarization, but in a more circumscribed way than many commentators suggest. Take first the question, of choice, and in particular, whether people seek out media choices that reinforce their existing beliefs. The answer is (perhaps not surprisingly) yes: Republicans are more likely to tune in to Fox News and liberals are more likely to watch MSNBC. Researchers have also found that these effects are stronger for those who are more partisan and politically involved.

But there is perhaps an even more important type of selection at work. While the political can tune into Fox and MSNBC, those who dislike politics also have more options than ever for avoiding it. In lieu of the nightly news—or a televised presidential address—they can watch Sports Center, Entertainment Tonight, or a rerun of The Big Bang Theory. When confronted with a political option, they simply change the channel to something else that they find more agreeable . Even the most popular cable news programs get 2 to 3 million viewers on a typical evening in a country of 300 million Americans. In earlier decades, some of these individuals would have been incidentally exposed to political news and information (by, say, watching the television news at 6 o’clock, when there were no other options). Now that they can avoid news altogether, they know less about politics and are less likely to participate . So the growth of media choice strengthens the extremes while hollowing out the center, making the electorate more divided.

But what about the effects of partisan media on those who do watch these programs? While this research tradition is still relatively young, scholars have found a number of effects: on vote choice, participation , and attitudes toward bipartisanship and compromise, among others. The research looking at effects on attitudes finds that while there are effects, they are concentrated primarily among those who are already extreme. This suggests that these programs contribute to polarization not by shifting the center of the ideological distribution, but rather by lengthening the tails (i.e., moving the polarized even further away from the center).

It is vital to put these effects into context. As noted above, these programs attract a small audience, but those who watch these shows are more partisan, politically interested, and politically involved; these are the individuals who are more likely to make their voices heard in the halls of power. So to the extent that these shows matter, it is by influencing this relatively narrow audience. These programs have few direct effects on most Americans.

While scholars have learned a great deal about how media might shape polarization, there are still many questions to be answered. First, we know essentially nothing about the indirect effects of these shows: do those who watch these shows transmit some of the effects to non-watchers through discussion in social networks? Does the Rachel Maddow fan in the cubicle next to you shape your opinions by telling you what she discussed on her show last night? Second, what is the effect of these shows on the broader media agenda, and on elites? Do the frames and issues that originate on Fox or MSNBC influence the broader media agenda? If so, that’s an important finding, as it shows how these networks help to shape what a wider swath of Americans see.

In general, we understand little about how news outlets influence one another, especially in a 24-hour news cycle. Some recent work suggests that these outlets (particularly Fox) have shaped the behavior of members of Congress. The work discussed here has focused on the effects of cable TV news (with similar effects found previously for political talk radio). But there is an even broader range of material on the Internet, and few works have yet explored these effects. How the Internet—and especially social media sites like Twitter and Facebook—contributes to polarization will be an important topic in the years to come.

Further Reading

This is the latest post in our ongoing series on political polarization. The previous posts are listed below. -Dan Hopkins

What we do know and don’t know about our polarized politics.

American politics is more competitive than ever. That’s making partisanship worse.

Polarization we can live with. Partisan warfare is the problem.

How political polarization creates stalemate and undermines lawmaking.

Electing more women to Congress isn’t a solution for polarization.

How U.S. state legislatures are polarized and getting more polarized (in 2 graphs).

How ideological activists constructed our polarized politics.

Our politics may be polarized. But that’s nothing new.

Our politics is polarized on more issues than ever before.

How race and religion have polarized American voters.

Can young voters break the cycle of polarization?

Americans aren’t polarized, just better sorted.

How politically moderate are Americans? Less than it seems.

The real extremists are American voters, not politicians.

How better educated whites are driving polarization.

How our partisan loyalties are driving polarization.

Party polarization is making is more prejudiced.

Why don’t Americans trust the government? Because the other party is in power.