In the first study, the team built a network of computers that closely watched 1,382 Chinese websites, tracking new posts about a variety of topics over periodic intervals to see if and when they were censored. 11 million posts covering 85 topic areas, ranging in political sensitivity from popular video games to the dissident artist Ai Weiwei, were chosen for investigation alongside online chatter resulting from real-world events. In the second study, King and his team went undercover. They created fake accounts on over 100 social media sites, submitted posts to see which ones were censored, and even set up their own social media site in China.

Two points stand out among their findings. First, China’s censorship infrastructure is incredibly efficient: Objectionable posts are removed with a near-perfect elimination rate and typically within 24 hours of their posting. The authors write, “This is a remarkable organizational accomplishment, requiring large scale military-like precision.”

Second, King and his team found that Chinese censors focus on posts that refer to, instigate, or are otherwise linked to grassroots collective action such as protests, demonstrations, and even apolitical mass activities, and that the regime seems comparatively more comfortable with criticism of the government. For example, this passage was not censored:

The Chinese Communist Party made a promise of democratic, constitutional government at the beginning of the war of resistance against Japan. But after 60 years that promise has yet to be honored. China today lacks integrity, and accountability should be traced to Mao. [...] intra-party democracy espoused today is just an excuse to perpetuate one-party rule.

Meanwhile this sentence, which refers to a suicide bomber whose homes were demolished, was nixed:

Even if we can verify what Qian Mingqi said on Weibo that the building demolition caused a great deal of personal damage, we should still condemn his extreme act of retribution....The government has continually put forth measures and laws to protect the interests of citizens in building demolition.

This isn’t to say that the Communist Party is happy with criticism. Chinese people can still be punished for publishing dissent, especially if it gains traction: For example, a man in Shaanxi Province was recently detained for being retweeted 500 times on Sina Weibo. But to the extent that criticism is expressed in small ways, it is secondary to writing that might incite collective action.

King suggests at least two reasons for this. First, allowing some criticism might mollify citizens who want to blow off some steam, thereby keeping them from expressing these feelings more violently. Second, this relative leniency is a useful way for the central government to learn about problems that require attention. King cites the political scientist Martin Dimitrov, who argues that “regimes collapse when its people stop bringing grievances to the state”—because they no longer see the state as legitimate. Calls to collective action, however, are regarded as dangerous and are not tolerated at all—even when they have little to do with politics.