Google’s policies in the area of filtering requests are not yet clear, he said, noting that the “American vision of free speech” may not be the final word in Google’s foreign policies.

“Google does not yet have a clear, well-articulated public policy,” Edelman agreed.

“We carefully consider any credible complaint on a case-by-case basis and take necessary action,” Google spokesperson Nathan Tyler told the Associated Press in a statement last week.

The report on Google filtering came in the midst of an ongoing Berkman study of China’s Internet blocking practices. Sharp-eyed “netizens” first alerted Zittrain and Edelman to discrepancies in French and German Google search results, and the two ran checks on other sites known or presumed to contain controversial material.

Their report, published at http://cyber.law.harvard.edu/filtering/google, is interactive—readers can view filtered sites and check in pop-up windows whether the sites are still banned on google.fr or google.de.

A few sites that once contained controversial material remain filtered, even though their content has changed or the domain is now empty.

“Blacklisting by Google continues long after,” said Edelman, adding that it is unclear how often, if ever, Google re-examines filtered sites.

The authors are currently asking the public to alert them to additional discrepancies in search results.

“We’re trying to get a sense of how much filtering is being done, how many resources are being put into the filtering,” Zittrain said.

They also plan to study Internet use in the United Arab Emirates, Vietnam and Spain.