Self-Censorship Under Law: A Case Study of The Hong Kong National Security Law

We study how aggressive legislation can increase self-censorship and alter online discourse, using Hong Kong's National Security Law as a case study. We collect a dataset of 7 million historical Tweets from Hong Kong users, supplemented with historical snapshots of Tweet streams collected by other researchers. We find that Hong Kong users demonstrate two types of self-censorship, and that the rate of self-censorship continues to increase. First, we find that Hong Kong users are more likely than a control group, sampled randomly from historical snapshots of Tweet streams, to remove past online activity. They are 35.74% more likely than this group to make their accounts private, and over two times as likely to delete past posts. We also find that since the passing of the National Security Law, Hong Kongers are continuing to speak less about politically sensitive topics that have been censored on social media platforms in mainland China.