The world knows that the Chinese government censors free speech. It's not a well-kept secret. But it turns out the Chinese government is much less concerned with what people say than with what they might do.

“You can say the most vitriolic-like things you want about the leaders of China and not be censored. But, if you call for any kind of collective action, whether for or against the government, that will be censored,” says Gary King, a professor of government at Harvard University and director of the Institute of Quantitative Social Science.

King says that before he began his study into Chinese censorship he and his co-authors Jennifer Pan and Molly Roberts all assumed what everybody else did: Chinese censors prune or eliminate any criticism of the state, its policies and its leaders. But that assumption was completely false.

King and his team stumbled upon much of this information by accident. “We were interested in studying automated text analysis, believe it or not,” King says. “We had no intention of studying China at all.”

But in the course of testing new techniques for analyzing massive amounts of text, including the billions of social media posts, King acquired a database of 11 million social media posts in Chinese. He wanted to find a way of “pushing the techniques until they [broke],” and what better way, he thought, than to try them in a different language?

As it happens, Pan and Roberts are both fluent in Chinese. At one point they came to King and said there must be something wrong with the data they had been given. When they looked more closely at the posts, they found that many of the them led to dead links, while others sent them to a page that said the post was “being investigated.” They soon realized that they were looking at millions of posts that either had already been deleted or were “under review” by the Chinese censors.

“We had the whole corpus of uncensored Chinese language social media posts that the Chinese people couldn’t read — but we could,” King says. So they thought, “Let’s forget that other paper and write one about Chinese censorship.”

To do this, King says, they had to operate like investigative journalists: they set up their own social media site within China. They bought a URL, rented server space and purchased software from Chinese companies to run the site. Once they were up and running, they spoke with customer support at these companies for advice on how to ‘censor’ their own site.

“They were pretty good at their job,” King says. “We would ask them questions like, ‘How would we stay out of trouble with the Chinese government? How does censorship work? What are we supposed to do?’ And their job was to help us.” Then the three researchers posted — and censored — their own submissions, while watching how the real Chinese censors worked.

King estimates there are about 100,000 to 200,000 censors within China, working at every level of government and within social media firms themselves. But there is a second way the Chinese censor, called an automated review. In this system, a post with certain keywords is automatically flagged and sent to a sort of "internet purgatory," where it sits until real censors can review it. “Instead of reading existing posts and deciding whether or not to take them down, they read the posts from the automated review process and decide whether or not to put them up,” King explains.

“The really interesting thing about the automated keyword process,” King says, “is that it is wholly ineffective. It does not work.” Chinese Internet users have apparently figured out creative ways to trick the system so that it doesn’t recognize certain keywords and flag the posts, he explains.

The Chinese are not remotely embarassed about censorship, King points out. They think it’s an important way to keep the country from falling into chaos. In fact, two animated characters, Jingjing and Chacha, often appear on web pages to remind citizens that they are being watched. But the individual censors themselves, he says, are just doing what they're told and don’t really see the big picture.

“We’ve seen the big picture — and it’s very, very clear to us in every method we've applied that they don’t censor criticism, and they do censor collective action. So, the Chinese people are individually free and collectively in chains with respect to their speech,” King concludes.

This story is based on an interview that aired on PRI's Science Friday with Ira Flatow