Our goal in this article is to accurately describe the social media consumption of a set of respondents, grouped by ideology. We do so at a granular level, presenting not only aggregate statistics, but providing a sense of the distribution and variety of online media consumption among individuals . Our aim is to identify how many people live in “bubbles”—and, in particular, how many people on the ideological poles live in bubbles. This has implications for one of the major political issues of our time: political polarization. If those on the left and right of center not only dwell in ideological cocoons but are unaware of what the other side sees, the concern is that those on opposite sides of the political spectrum will continue to misunderstand each other and rely on crude stereotypes, leading to further cycles of negative partisanship.

To investigate these hypotheses, we build on recent work concerning online selective exposure (e.g., Bakshy, Messing, & Adamic, 2015 ; Flaxman, Goel, & Rao, 2016 ; Gentzkow & Shapiro, 2011 ; Guess, 2018 ; Messing & Westwood, 2014 ) by examining the degree to which exposure to diverse opinions and content on social media varies among individuals across the ideological spectrum. To do so, we use a large survey of social media users with Twitter accounts. Our focuses are threefold. First, we examine the ideological distributions of the accounts that users follow , disaggregated by whether such accounts are (a) members of the news media, (b) part of the political class, or (c) non-elites (the general public). Second, we examine the ideological distributions of the tweets that users receive , overall and from each of these account types. Finally, we examine whether the retweets that users receive originate from accounts that are more ideologically diverse or more ideologically moderate than the tweets that users receive from those they follow directly. This permits us to examine the extent to which indirect exposure to people outside of one’s immediate network serves as a mechanism to expand the diversity of the opinions and media consumed on social media.

On the contrary, while the above democratizing account of the Internet and social media is primarily a story of information supply, the story regarding the formation of ideological bubbles concerns information demand. Despite the relatively widespread availability of ideologically diverse information, individuals may nevertheless choose to selectively expose themselves only to material and individuals who are ideologically similar. Such an account is grounded, first, in the well-known empirical regularity of homophily, the tendency of individuals to associate with others who are similar to themselves (see McPherson, Smith-Lovin, & Cook, 2001 ), and second, by work demonstrating that the public frequently engages in selective exposure, the tendency to consume information that ideologically aligns with one’s own political beliefs (see Stroud, 2010 ). Under this account, one might hypothesize that many among the public would be exposed only to an ideologically narrow range of content, a consequence both of the individuals they associate with online and the material they choose to consume.

In addition to increasing choice , the advent of social media may also have led to an increase in incidental exposure to ideological heterogeneous information (e.g., Barberá, 2015b ; Brundidge, 2010 ; Feezell, 2018 ; Fletcher & Nielsen, 2018 ; Messing & Westwood, 2014 ). Although many people may not explicitly seek to consume such content, the sharing mechanism of social networks such as Facebook and Twitter may result in many among the public being exposed to political information they did not seek out, including information that is not consistent with their own ideological predilections. Thus the structure of social media could indirectly prevent ideological bubbles from forming. As a consequence, the relative ease of access to and abundant supply of ideologically diverse information sources, and the potential for indirect exposure to such content, lead to the hypothesis that relatively few among the public will inhabit ideological echo chambers online.

For social scientists, the connection between social media and the prevalence of online ideological bubbles is not clear either theoretically or empirically. 1 The arguments concerning the role of the Internet and social media in the consumption of ideologically diverse content can lead to hypotheses that run in opposite directions, predicting both the presence and absence of ideological bubbles. News media in the United States during the last half-century has itself become increasingly ideologically diverse. Before the advent of the Internet, the news media landscape underwent a rapid shift from having three ideologically similar networks to a landscape with a wider range of diverse cable networks, some without any news content at all. This gave individuals the choice to opt in to news with a distinct ideological slant, or to opt out entirely ( Prior, 2007 ). The adoption of broadband Internet and social media has led the news and political information landscape to be diversified further, with increased access to heterogeneous political information sources now available to the vast majority of the public. These changes have democratized both the production and consumption of political and social information ( Benkler, 2006 ) and increased opportunities for the public to consume ideologically heterogeneous political information.

In this article, we measure the ideological distribution of both Twitter accounts followed and tweets potentially seen at the individual level. We analyze data from a nationally representative survey of Americans with linked data on respondents’ Twitter IDs, which allows us to collect the set of accounts that they followed and all tweets posted by those accounts. We quantify how many respondents live in online ideological “bubbles” based on their own self-reported ideology. We find a substantial amount of overlap in the ideological distributions of accounts followed by users on opposite ends of the political spectrum. In addition to this relative similarity in overall following patterns, however, many individuals’ willingness to purposefully venture into challenging spaces is limited, although an analysis encompassing all potentially seen tweets shows approximately twice as much cross-cutting exposure—an effect that is somewhat larger when focusing on retweets from other accounts. The individual-level pattern also appears to be asymmetric: When compared with fixed points on the ideological continuum, conservatives are more likely to follow accounts at or to the left of MSNBC than liberals are to follow accounts at or to the right of Fox News, even though the measure of ideological slant we employ places the two outlets at roughly equidistant positions from the midpoint.

Does social media encourage the public to live in online ideological “echo chambers,” consuming and sharing only information that is consistent with their political beliefs? This question has received increasing attention by political commentators and politicians. Some have claimed, for example, that such ideological echo chambers on social media are “destroying democracy” ( El-Bermawy, 2016 ); explain “why Trump won and [we] didn’t see it coming” ( Baer, 2016 ); and create “angry, poorly informed partisans” ( Lee, 2016 ). Former President Barack Obama has suggested, furthermore, that ideological echo chambers are now a critical issue for democracy. “One of the dangers of the Internet is that people can have entirely different realities,” he warned. “They can be cocooned in information that reinforces their current biases” ( Yeginsu, 2017 ). Much of the public discourse concerning social media appears to suggest a belief that online ideological echo chambers are both highly pervasive and deeply problematic for society.

In addition to aggregate comparisons of the accounts followed and the tweets received by survey respondents, we further categorize accounts that are followed into three types: (a) media elite, (b) political elite, and (c) non-elite (i.e., the mass public). Accounts defined as the media and political elite include the accounts of major media organizations, journalists, and politicians in the United States. “Non-elites” are therefore defined as the set of all Twitter accounts not included among the list of media and politicians. 4

To measure the political ideology of the accounts that the YouGov respondents follow and the tweets that they receive, we use estimates derived from the method developed by Barberá (2015a) . The method is based on the assumption that Twitter users signal their political ideology by the accounts of media organizations, journalists, and politicians that they follow on Twitter. Users who follow primarily conservative politicians and conservative news media, for example, are assumed to be more likely to themselves be conservative than others who follow more ideologically moderate or liberal political actors. This assumption follows from the fact that individuals tend to associate with those who are similar to themselves, a regularity often referred to as homophily ( McPherson et al., 2001 ). More technically, the model is similar to an item-response model in which the probability that a user follows a political actor’s Twitter account is a function of the latent (ideological) spatial distance between the user and that political actor. The method has been used in recent work to examine selective exposure ( Barberá, Jost, Nagler, Tucker, & Bonneau, 2015 ; Vaccari et al., 2016 ), to compare ideological estimates of political actors derived from social media to those from other data sources ( Tausanovitch & Warshaw, 2017 ), and to examine the link between journalists’ social media networks and the content they produce ( Wihbey, Coleman, Joseph, & Lazer, 2017 ). Given the size of the Twitter data collected, for computational reasons our ideology estimates are approximated using correspondence analysis ( Barberá et al., 2015 ; Greenacre, 2007 ).

To examine the relationship between the ideology of Twitter users and the amount of exposure to ideologically diverse content, we need to measure both the ideology of our survey respondents and that of the accounts respondents follow and from whom they receive tweets. To measure respondent ideology, survey respondents were asked to locate themselves on an integer-valued ideological placement scale that ranged from 0 ( liberal ) to 100 ( conservative ). To ease presentation, we group respondents into ideological quintiles. This permits simpler interpretations of comparisons both between and within ideological categories. However, because we group by quintile, it is important to note that we are referring to each group’s relative ideological rank among all Twitter users in the sample (ranges of the ideological self-placement variable that define these quintiles are presented in the Appendix ). We also supplement our analysis by examining the left- and right-most 5% of the self-placement distribution to investigate behavior on the ideological extremes.

To measure ideological exposure on Twitter, we use data from a representative sample of Twitter users who are located in the United States and who were surveyed by the research firm YouGov during the 2016 U.S. election campaign. 2 For each respondent for whom we have data on accounts followed ( N = 1 , 496 ; 642,345 total unique accounts), we collected the most recent 3,200 tweets sent by each of those accounts (~1.2 billion tweets in total). 3 In sum, our data contain all accounts followed and the most recent tweets potentially seen by our YouGov sample during and prior to 2016.

Results

We begin by examining the number of politicians and media accounts that respondents follow on Twitter, both overall and by ideological quintile. If the average Twitter user in the United States follows very few or no media and/or political accounts, we might conclude that few reside in ideological bubbles simply because many choose not to use Twitter to receive political news at all.5 In Table 1, we show the proportions of respondents who follow a given number of media and political accounts. As the table demonstrates, over one third of respondents (40%) follow no media accounts at all; over half (53%), no political accounts. There appears, however, to be a relatively large proportion of respondents who follow many of each: 18% of respondents follow 11 or more media accounts and 7% follow 11 or more political elites. To the extent that one third of Twitter users are not following any media accounts, we know that those users will only be in a “bubble” online if many of their friends share political information with them. We also examine whether stronger partisans are more likely to follow more media and political accounts than moderates by calculating the average number of accounts followed among those in each ideological quintile. Results are presented in Table 2. As expected, the average number of media accounts and political accounts followed by those on the ideological extremes is greater than those in the three middle quintiles. In other words, those on the ideological extreme are more politically engaged in their following behavior on Twitter than are moderates.

Table 1. Number of Media and Political Accounts Followed.

Table 2. Average Number of Media and Political Accounts Followed—by Quintile.

Next, we examine the ideological distribution of media accounts that are followed by our respondents, and compare this distribution to the ideological distribution of all media accounts. This comparison permits us to examine the extent to which users follow media accounts across the ideological spectrum proportional to the availability of media accounts across that spectrum. To investigate this, we show in Figure 1 the ideological distribution of all media accounts and the media accounts followed by our respondents weighted by the frequency by which they are followed. Well-known media accounts are labeled to provide context to the distribution. As the figure shows, accounts around and to the right of Fox News are overrepresented in the distribution of media accounts followed relative to the ideological distribution of all media accounts available, and the distribution of media followed appears bimodal.6

We now examine whether and to what degree the following of media accounts varies by respondents’ ideology. If all liberals were to follow only liberal media sources, and all conservatives were to follow only conservative media sources, then it would constitute clear evidence that people generally reside in ideological echo chambers. To investigate this, we graph the distributions of media accounts followed by respondents in each ideological quintile in Figure 2. The figures show that, as one would expect, respondents in the most liberal quintile follow a more liberal set of media accounts than do respondents in the most conservative quintile. There is, however, substantial overlap in the ideology of media accounts followed across quintiles. Each group, for instance, follows media accounts both to the right and left of the New York Times, though this region is much smaller for the most conservative quintile. Furthermore, each ideological group’s distribution covers considerable area bounded by MSNBC on the left and the Wall Street Journal on the right. However, we also observe that the two most conservative quintiles have distributions with two modes: one in this common (mainstream) center and another mode on the right between Fox News and Breitbart. We examine this feature at the individual level further below.

For comparison, in Figure 3 we plot the ideological distribution of politicians followed by respondents in each quintile. Here we see much clearer separation: Respondents in the two right- and left-most quintiles clearly choose to follow politicians who are to the left or right of the zero point, and in fact they predominantly follow politicians to the left of Clinton (lower quintiles) and to the right of Trump (upper quintiles). We also present, in Figure 4, the ideological distribution of non-elite accounts followed by respondents in each quintile. For respondents in the most conservative quintile, the distribution of non-elite accounts is similar to the distribution of political accounts, with two modes and the bulk of accounts followed to the right of Trump. One point to be made by comparing these three figures is that following of media accounts is less polarized than is following of political and non-elite accounts. This suggests that many people are likely following media sources that are more moderate on average than the friends or politicians they follow.

To present these data differently, in Table 3 we select descriptive (fixed) cut-points to provide meaningful context for the distributions of media accounts followed by respondents based on their ideological ranking. In each of the five quintiles, we give the proportion of all media accounts followed to the left or right of well-known media accounts by aggregating over all respondents.7 In addition to the five quintiles, we also include the left-most 5% of respondents and right-most 5% of respondents. In the second row of Table 3, we show that 29% of all media accounts followed by liberals (those in the left-most quintile) are at least as far to the left as MSNBC (i.e., MSNBC or media accounts to the left of MSNBC), while only 4% of media accounts followed by liberals are at least as far to the right as Fox News. Another way of stating these results is that for the most liberal quintile, 71% of media accounts followed are to the right of MSNBC. However, virtually all of those accounts are also to the left of Fox News (the proportion of media accounts followed by this group that is as far to the right as Breitbart or beyond is 0). If we look at the second-left-most quintile of respondents, we still see only 1% of accounts followed are as far to the right as Breitbart and only 5% are as far to the right as Fox News.

Table 3. Proportion of Media Accounts Followed to the Left or Right of Well-Known Media Accounts.

When we look at the most conservative quintile of respondents, we see that an analogous share of followed accounts as above, 6%, are at least as far to the left as MSNBC. If we look at the next most conservative quintile, 9% of the media accounts respondents in that group follow are at least as far to the left as MSNBC. On the contrary, 50% of media accounts followed by those in the most conservative quintile are at least as far to the right as Fox News, suggesting greater concentration in following behavior among that group. Furthermore, 12% of media accounts followed by those in that group are at least as far to the right as Breitbart—roughly the same share as that followed by respondents in the most conservative 5%.

Next, we turn to an analysis at the individual level. We define a respondent to be in a “bubble” if he or she is a liberal who does not follow a minimal proportion of conservative media accounts, or a conservative who does not follow a minimal proportion of liberal media accounts. In Table 4, we report the proportion of respondents in each ideological group who follow accounts in each range. The threshold we use in the table is to calculate the proportion of people whose media diet includes at least 5% of followed accounts in one of the ranges identified (e.g., at least 5% of accounts followed are to the left of MSNBC). As the majority of respondents follow fewer than 20 media accounts, for most respondents this threshold simply requires them to follow at least one account in a given range. Since, as we saw, many of our respondents follow zero media accounts on Twitter, we report the proportion of respondents conditioning on following at least one media account.

Table 4. Proportion of Respondents for Whom at Least 5% of Media Accounts Followed Are to the Left or Right of Well-Known Media Accounts.

If we look at the second row of Table 4, we see that 78% of those among the most liberal quintile of respondents who follow at least one media account have media diets in which at least 5% of the accounts they follow are at least as far to the left as MSNBC. More interestingly, we can see that only 1% of people in the most liberal quintile have media diets with 5% of followed accounts at least as far to the right as Breitbart, and only 16% of people in the most liberal quintile follow accounts at least as far to the right as Fox News. Thus if we think that for a liberal to never venture as far right as Fox News is to be in a bubble, 84% of respondents in the most liberal quintile are in a bubble (as are 85% in the second most liberal quintile). However, if we look at the respondents in the most conservative quintile, we see that 22% have a media diet that includes sources at least as far to the left as MSNBC. By the same logic above, this would imply that 78% of people in the most conservative quintile are in a bubble. However, if we look at the people in the right tail of the distribution (right-most 5%), we see an a higher proportion of them following accounts at least as far to the left as MSNBC: 42% of respondents in the right-most 5% of the ideological distribution follow media accounts at least as far to the left as that account.

One potential explanation for the asymmetric following behavior of liberals and conservatives shown above is that it is a function of asymmetries in the supply of and demand for news: People across the political spectrum find reason to follow the output of mainstream news organizations committed to norms of journalistic professionalism and equipped with newsrooms and reporting resources, even as these publications are perceived by some to be left-leaning and are trusted more highly by those on the left of center than those on the right (see Grossmann & Hopkins, 2016). Ideologically committed conservatives may have more of a demand for ideologically congenial content in addition to mainstream news due to these perceptions, while liberals are more likely to be satisfied with traditional sources of journalism.

If true, we should see a more symmetric distribution when we look at the accounts of politicians followed. Thus in Table 5, we look at the set of politicians respondents follow, and see how many respondents follow politicians with viewpoints likely to be different than their own. Here we adopt politicians (Bernie Sanders, Hillary Clinton, Donald Trump, and Ted Cruz) as cut-points rather than media outlets. We see that most liberals still do not venture right: Only 16% of those in the left-most quintile who follow any politicians follow one such account at least as far to the right as Donald Trump, and only 8% follow a politician at least as far to the right as Ted Cruz. And we again see that conservatives are more likely to go left than liberals are to go right: Of respondents in the most conservative quintile who follow at least one politician, 35% follow a politician at least as far to the left as Hillary Clinton. Thus, our earlier result does not seem to be based on extraneous factors; conservatives on Twitter seem more inclined to look left than liberals do to look right.

Table 5. Proportion of Respondents for Whom at Least 5% of Politicians’ Accounts Followed Are to the Left or Right of Well-Known Politicians’ Accounts.

In Table 6, we examine the set of non-elites followed. We see that 41% of liberals follow non-elite accounts at least as far to the right as Fox News, while 66% of conservatives follow non-elite accounts at least as far to the left as MSNBC. This of course suggests that 59% of liberals are living in “bubbles” with respect to the non-elite accounts they follow. For conservatives, only 34% of them are evidently in such bubbles. Again, this is consistent with our previous results.

Table 6. Proportion of Respondents for Whom at Least 5% of Non-Elite Accounts Followed Are to the Left or Right of Well-Known Media Accounts.

While following activity arguably reflects some form of conscious intent, another way to measure whether or not respondents are in bubbles is to consider the sources of tweets they actually receive. We saw in Table 4 that liberals did not follow many right-leaning media accounts. However, if we count tweets potentially seen from media accounts based on ideology, things look somewhat different. Table 7 shows the proportion of tweets from media sources that are to the left or right of well-known accounts (an analogous table for the subset of users who follow at least one media account is provided in the Appendix). Whereas in Table 4 we saw that 16% of respondents in the most liberal quintile followed accounts at least as far to the right as Fox News, here we see that 27% of those in the most liberal quintile do get some share of their Twitter news diet from tweets at least as far to the right as Fox News. And while 22% of conservatives chose to follow media accounts at least as far to the left as MSNBC, 43% get some part of their media diet of tweets from sources at least as far to the left as that source. If we instead look at the proportion of politicians’ tweets in respondents’ feeds (Table 8), we again see that liberals and conservatives appear to have a more balanced information diet than if we simply look at following behavior.

Table 7. Proportion of Respondents for Whom at Least 5% of Tweets Seen From Media Accounts Followed Are to the Left or Right of Well-Known Media Accounts.

Table 8. Proportion of Respondents for Whom at Least 5% of Tweets Seen From Politicians’ Accounts Followed Are to the Left or Right of Well-Known Politicians’ Accounts.

Finally, if we look at tweets that came from non-elite accounts, we see a more balanced distribution. In Table 9, we plot proportions of respondents with tweet diets sent by non-elites falling within ranges defined by our anchor media outlets from above. These diets are more ideologically balanced than those comprising politicians or media accounts.8 Although the difference here is not as stark as it was for media or political accounts followed versus tweets seen.

Table 9. Proportion of Respondents for Whom at Least 5% of Tweets Seen From Non-Elites Are to the Left or Right of Well-Known Media Accounts.

Comparing Online and Offline Media Exposure If we want to study whether or not people are in information bubbles overall, there is no reason to restrict the content of interest to what people consume online.9 If conservatives choose to follow nothing to the left of Breitbart on Twitter but watch the CBS Evening News every night, then they are not in ideological bubbles—they have as much exposure to mainstream news as their pre–Internet-age parents did, and are merely supplementing it with the alternative viewpoint provided by Breitbart. In the survey, we therefore asked our respondents, “Do you watch news shows on any of the following networks, and if so, how often?” Response options were arranged in a grid with Fox News, CNN, MSNBC, CBS, ABC, and NBC as the network options, and “every day,” “several times a week,” “at least once a week,” “less than once a week,” and “never” as available frequencies.10 We then look to see what proportion of conservatives in ideological bubbles on Twitter (i.e., less than 5% of the accounts they follow are at least as far to the left as MSNBC) diversified their media diets by watching news on one of the major networks at least once a week. Above we reported that 78% of conservatives do not go as far left as MSNBC on their following behavior on Twitter. However, 14% of that group of conservatives in ideological bubbles on Twitter did report watching left-leaning TV news (MSNBC). If we take these responses at face value and assume that network television is to “the left of” conservative media, we reduce by almost a factor of two the proportion of conservatives who live in “media bubbles.” However, even with this adjustment, we still have 67% of self-identified conservatives with a media diet that does not stray as far to the left as MSNBC. If we apply a similar adjustment to our liberal respondents in ideological bubbles on Twitter (i.e., those for which less than 5% of the accounts they follow are at least as far to the right as Fox News), the effect is much smaller. Only 7% of liberal respondents who chose to be in ideological “bubbles” on Twitter report watching Fox News on television: Thus, we would revise our estimate of the number of liberals in ideological bubbles from 84% to 78%.11 This “correction” for offline media exposure becomes more important if we had chosen our bubbles more restrictively. Say we defined a conservative to be in an ideological bubbles if fewer than 5% of the accounts they followed were to the left of the Wall Street Journal. Of the conservatives in our sample, 44% were in such conservative extreme-bubbles. However, 46% of those watched at least one of either MSNBC, CNN, ABC, CBS, or ABC. Thus if we consider a larger part of their total media diet, online and television, we would estimate that only 24% of conservatives were in extreme media bubbles.