An increasing amount of attention has been devoted to the problem of "toxic" or antisocial behavior on social media. In this paper we analyze such behavior at very large scales: we analyze toxicity over a 14-year time span on nearly 500 million comments from Reddit and Wikipedia, grounded in two different proxies for toxicity. At the individual level, we analyze users' toxicity levels over the course of their time on the site, and find a striking reversal in trends: both Reddit and Wikipedia users tended to become less toxic over their life cycles on the site in the early (pre-2013) history of the site, but more toxic over their life cycles in the later (post-2013) history of the site. We also find that toxicity on Reddit and Wikipedia differ in a key way, with the most toxic behavior on Reddit exhibited in aggregate by the most active users, and the most toxic behavior on Wikipedia exhibited in aggregate by the least active users. Finally, we consider the toxicity of discussion around widely-shared pieces of content, and find that the trends for toxicity in discussion about content bear interesting similarities with the trends for toxicity in discussion by users.

翻译：社交媒体上的"有害"或反社会行为问题日益受到关注。本文通过两个不同的有害行为代理指标，在极大规模上对此类行为进行分析：我们研究了Reddit和维基百科近5亿条评论中跨越14年的有害行为演变。在个体层面，我们分析了用户在平台使用期间的有害程度变化，发现了一个显著的趋势逆转：在平台早期（2013年前）历史中，Reddit和维基百科用户在其生命周期内都趋向于减少有害行为；而在平台后期（2013年后）历史中，用户在其生命周期内反而趋向于增加有害行为。我们还发现Reddit和维基百科的有害行为存在关键差异：Reddit上最具危害性的行为总体上由最活跃的用户呈现，而维基百科上最具危害性的行为总体上由最不活跃的用户呈现。最后，我们考察了广泛传播内容讨论中的有害性，发现内容讨论的有害趋势与用户讨论的有害趋势存在有趣的相似性。