Ca' Foscari University of Venice, Via Torino 155, 30172 Venice, Italy.
ISC-CNR, SC-CNR, Sapienza University of Rome, Via dei Taurini 19, 00185 Rome, Italy.
Vaccine. 2018 Jun 14;36(25):3606-3612. doi: 10.1016/j.vaccine.2018.05.040.
Vaccine hesitancy has been recognized as a major global health threat. Having access to any type of information in social media has been suggested as a potential influence on the growth of anti-vaccination groups. Recent studies w.r.t. other topics than vaccination show that access to a wide amount of content through the Internet without intermediaries resolved into major segregation of the users in polarized groups. Users select information adhering to theirs system of beliefs and tend to ignore dissenting information.
The goal was to assess whether users' attitudes are polarized on the topic of vaccination on Facebook and how this polarization develops over time.
We perform a thorough quantitative analysis by studying the interaction of 2.6 M users with 298,018 Facebook posts over a time span of seven years and 5 months. We applied community detection algorithms to automatically detect the emergence of communities accounting for the users' activity on the pages. Also, we quantified the cohesiveness of these communities over time.
Our findings show that the consumption of content about vaccines is dominated by the echo chamber effect and that polarization increased over the years. Well-segregated communities emerge from the users' consumption habits i.e., the majority of users consume information in favor or against vaccines, not both.
The existence of echo chambers may explain why social-media campaigns that provide accurate information have limited reach and be effective only in sub-groups, even fomenting further opinion polarization. The introduction of dissenting information into a sub-group is disregarded and can produce a backfire effect, thus reinforcing the pre-existing opinions within the sub-group. Public health professionals should try to understand the contents of these echo chambers, for example by getting passively involved in such groups. Only then it will be possible to find effective ways of countering anti-vaccination thinking.
疫苗犹豫已被认为是一个主要的全球健康威胁。人们可以在社交媒体上获取任何类型的信息，这被认为是助长反疫苗群体发展的一个潜在因素。最近的研究表明，与疫苗接种以外的其他话题相比，通过互联网获取大量内容而无需中介会导致用户在两极分化的群体中严重分化。用户选择符合其信仰体系的信息，往往会忽略不同的信息。
评估用户在疫苗接种问题上的态度是否在 Facebook 上两极分化，以及这种两极分化是如何随着时间的推移发展的。
我们通过研究 260 万用户在七年零五个月的时间内与 298018 个 Facebook 帖子的互动，进行了全面的定量分析。我们应用社区检测算法自动检测社区的出现，这些社区解释了用户在页面上的活动。此外，我们还量化了这些社区随时间的凝聚力。
我们的研究结果表明，疫苗内容的消费主要受到回音壁效应的影响，而且这种两极分化随着时间的推移而增加。从用户的消费习惯中出现了分隔良好的社区，即大多数用户要么消费支持疫苗的信息，要么消费反对疫苗的信息，而不是两者兼而有之。
回音壁的存在可以解释为什么提供准确信息的社交媒体活动影响力有限，只能在亚群体中有效，甚至进一步加剧意见的两极分化。向亚群体中引入不同意见会被忽视，并可能产生反向反应，从而强化亚群体内部原有的观点。公共卫生专业人员应该尝试理解这些回音壁的内容，例如通过被动参与这些群体。只有这样，才能找到对抗反疫苗思维的有效方法。
