Economic growth depends on an ability to access relevant information. Although censorship prevents access to certain information, the direct consequences of censorship are well-known and somewhat predictable. For example, blocking access to Falun Gong literature is unlikely to harm a country’s consumer electronics industry. On the web, however, information of all types is interconnected. Blocking a web page might have an indirect impact reaching well beyond that page’s contents. To understand this impact, let’s consider how search results are affected by censorship.

Search engines keep track of what’s available on the web and suggest useful pages to users. No comprehensive list of web pages exists, so search providers check known pages for links to unknown neighbors. If a government blocks a page, all links from the page to its neighbors are lost. Unless detours exist to the page’s unknown neighbors, those neighbors become unreachable and remain unknown. These unknown pages can’t appear in search results — even if their contents are uncontroversial.

When presented with a query, search engines respond with relevant known pages sorted by expected usefulness. Censorship also affects this sorting process. In predicting usefulness, search engines consider both the contents of pages and the links between pages. Links here are like friendships in a stereotypical high school popularity contest: the more popular friends you have, the more popular you become. If your friend moves away, you become less popular, which makes your friends less popular by association, and so on. Even people you’ve never met might be affected.

“Popular” web pages tend to appear higher in search results. Censoring a page distorts this popularity contest and can change the order of even unrelated results. As more pages are blocked, the censored view of the web becomes increasingly distorted. As an aside, Ed notes that blocking a page removes more than just the offending material. If censors block Ed’s site due to an off-hand comment on Falun Gong, he also loses any influence he has on information security.

These effects would typically be rare and have a disproportionately small impact on popular pages. Google’s emphasis on the long tail, however, suggests that considerable value lies in providing high-quality results covering even less-popular pages. To avoid these issues, a government could allow limited individuals full web access to develop tools like search engines. This approach seems likely to stifle competition and innovation.

Countries with greater censorship might produce lower-quality search engines, but Google, Yahoo, Microsoft, and others can provide high-quality search results in those countries. These companies can access uncensored data, mitigating the indirect effects of censorship. This emphasizes the significance of measures like the Global Network Initiative, which has a participant list that includes Google, Yahoo, and Microsoft. Among other things, the initiative provides guidelines for participants regarding when and how information access may be restricted. The effectiveness of this specific initiative remains to be seen, but such measures may provide leading search engines with greater leverage to resist arbitrary censorship.

Search engines are unlikely to be the only tools adversely impacted by the indirect effects of censorship. Any tool that relies on links between information (think social networks) might be affected, and repressive states place themselves at a competitive disadvantage in developing these tools. Future developments might make these points moot: in a recent talk at the Center, Ethan Zuckerman mentioned tricks and trends that might make censorship more difficult. In the meantime, however, governments that censor information may increasingly find that they do so at their own expense.