Researchers in Carnegie Mellon University's School of Computer Science analyzed millions of Chinese microblogs, or "weibos" and found individual messages containing such terms were often deleted at rates that could vary based on current events or geography.
The study is the first large-scale analysis of political content censorship in social media, a controversy highlighted by Twitter's announcement earlier this year of a country-by-country policy for removing tweets that don't comply with local laws.
In China the researchers found that oft-censored terms included well-known hot buttons such as Falun Gong, a spiritual movement banned by the Chinese government, and human rights activists such as Ai Weiwei and Liu Xiaobo.
The study also found high rates of weibo censorship in certain provinces, notably Tibet, a hotbed of political unrest.
In Tibet up to 53 percent of locally generated microblogs were deleted by authorities, it found.
"A lot of studies have focused on censorship that blocks access to Internet sites, but the practice of deleting individual messages is not yet well understood," researcher Noah Smith said in a university release. "The rise of domestic Chinese microblogging sites has provided a unique opportunity to systematically study content censorship in detail."