Every day 4,200 Chinese media censors take a break during the evening news

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Here’s a tip for the 300 million users of China’s Twitter-like microblogging site Sina Weibo: If you don’t want to get censored, post your messages at around 7pm, Beijing-time.

In a study released this week, researchers monitoring 3,500 users for 15 days last year, tracking when their posts were deleted. Weibo censors work by deleting the 140 character posts after they’ve been published, usually because they refer to sensitive political issues.

The researchers concluded that most censors are working in real-time. While about 90% of deleted posts were taken down within 24 hours of the message being posted, the majority of deletions occurred within an hour of posting—and fully 30% were zapped within a minute of posting. To handle the roughly 70,000 posts that flood the site per minute, the company probably employs about 4,200 censors, if they work working eight hour shifts.

These censors are monitoring and deleting posts around the clock, often very late at night, the study notes. But there are two noted dips: one at around 7pm, when the national news is on, and again early in the morning, when most of the country is asleep. You can see that trend in this chart from the study:

Note that “child” post refers to a repost, while a “regular” post is one that was not reposted.
Note that “child” post refers to a repost, while a “regular” post is one that was not reposted.
Image: "The Velocity of Censorship: High-Fidelity Detection of Microblog Post Deletions"

And just what gets censored? We’ve reported before on the blocking of posts that bring up political scandals, such as the wealth of outgoing premier Wen Jiabao’s family or China’s new leader, Xi Jinping. Yet others, like the sex tape of a low-ranking official in Chongqing, were not. Between July and August of last year, the period the researchers monitored, commonly deleted posts included phrases such as “support Syrian rebels,” “freedom of speech,” “judicial independence,” “one-child policy abuse,” and “group sex.” Other terms like “Beijing,” “government,” “policeman,” and “people” were also common in deleted posts, the researchers note. And that breadth of topics would indeed keep censors quite busy—except when the evening news is on, that is.