To be fair, you can easily do the same with any number of other search engines (e.g. Yahoo). In fact, the original metric that you've proposed isn't very useful

To be fair, you can easily do the same with any number of other search engines (e.g. Yahoo). In fact, the original metric that you've proposed isn't very useful because the same search terms mean different things in different languages. For instance, in China the Tiananmen Square protests are called the "June Fourth Incident" (literally: 六四事件) so comparing a search for an English phrase with the same phrase on google.cn might not be meaningful. If you really just want to know what topics are being censored, there are a number of human rights organizations and non-profits that track such things.