The growing prominence of social media in public discourse has led to a greater scrutiny of the quality of online information and the role it plays in amplifying political polarization. However, studies of polarization on social media platforms like Twitter have been hampered by the difficulty of collecting data about the social graph, specifically follow links that shape the echo chambers users join as well as what they see in their timelines. As a proxy of the follower graph, researchers use retweets, although it is not clear how this choice affects analysis. Using a sample of the Twitter follower graph and the tweets posted by users within it, we reconstruct the retweet graph and quantify its impact on the measures of echo chambers and exposure. While we find that echo chambers exist in both graphs, they are more pronounced in the retweet graph. We compare the information users see via their follower and retweet networks to show that retweeted accounts share systematically more polarized content. This bias cannot be explained by the activity or polarization within users' own follower graph neighborhoods but by the increased attention they pay to accounts that are ideologically aligned with their own views. Our results suggest that studies relying on the retweet graphs overestimate the echo chamber effects and exposure to polarized information.

翻译：社交媒体在公共讨论中的日益突出地位，使人们更加关注在线信息的质量及其在加剧政治极化中的作用。然而，研究Twitter等社交媒体平台上的极化现象一直受到数据收集困难的阻碍，特别是关于社交图谱的数据，即塑造用户加入的回音室及其在时间线上所见内容的关注链接。研究者将转发行为作为关注者图谱的替代指标，但尚不明确这一选择如何影响分析。通过使用Twitter关注者图谱样本及用户在其上发布的推文，我们重建了转发图，并量化了其对回音室和曝光度测量的影响。虽然我们发现两种图谱中都存在回音室，但它们在转发图中更为显著。我们比较了用户通过关注者网络和转发网络所看到的信息，结果显示被转发的账户系统性地传播了更极化的内容。这种偏差无法用用户自身关注者图谱邻域内的活动或极化程度来解释，而是源于用户对与自己意识形态一致账户的更高关注度。我们的研究结果表明，依赖转发图的研究会高估回音室效应和极化信息的曝光度。