In early 2021, the stock prices of GameStop, AMC, Nokia, and BlackBerry experienced dramatic increases, triggered by short squeeze operations that have been largely attributed to Reddit's retail investors. These events showcased, for the first time, the potential of online social networks to catalyze financial collective action. How, when and to what extent Reddit users played a role in driving up these prices, however, remains unclear. We address these questions by statistical analysis of time series with high temporal resolution, about social activity on Reddit and Twitter as well as stock trading volumes. We find that increasing Reddit discussions anticipated high trading volume before the GameStop short squeeze, with their predictive power being particularly strong on hourly time scales. This effect emerged abruptly a few weeks before the event, but waned once the community of investors gained widespread visibility through Twitter. Meanwhile, the collective investment of the Reddit community, quantified through each user's financial position on GameStop, closely mirrored the market capitalization of the stock. These evidences suggest a coordinated action by Reddit users in developing a shared financial strategy through social media. Towards the end of January, users talking about GameStop contributed to raise the popularity of BlackBerry, AMC and Nokia, which emerged as the most popular stocks as the community gained global recognition. Overall, our results shed light on the dynamics behind the first large-scale financial collective action driven by social media users.

翻译：2021年初，GameStop、AMC、诺基亚和黑莓的股价经历了戏剧性上涨，这主要由轧空操作引发，而该操作普遍归因于Reddit的散户投资者。这些事件首次展示了在线社交网络催化金融集体行动的潜力。然而，Reddit用户在何时、以何种方式、在多大程度上推动了这些价格上涨，仍不明确。我们通过对Reddit和Twitter社交活动及股票交易量的高时间分辨率时间序列进行统计分析来探讨这些问题。研究发现，在GameStop轧空事件发生前，Reddit讨论量的增长预示了高交易量，其预测能力在小时时间尺度上尤为显著。这种效应在事件发生前几周突然出现，但在投资者社区通过Twitter获得广泛关注后逐渐减弱。同时，通过每位用户在GameStop上的持仓量来量化的Reddit社区集体投资行为，与股票市值变化高度吻合。这些证据表明Reddit用户通过社交媒体协调行动，形成了共同的金融策略。到1月下旬，讨论GameStop的用户助推了黑莓、AMC和诺基亚的热度——随着该社区获得全球关注，这些股票成为最受追捧的投资标的。总体而言，我们的研究揭示了首次由社交媒体用户驱动的大规模金融集体行动背后的动态机制。