Google has announced a change to its search algorithm that reduces rankings for low-quality sites.

The changes, implemented in the last few days, impacts about 11.8 percent of Google’s queries, Google’s Amit Singhal and Matt Cutts wrote in a blog post. The duo defined low-quality sites as those that are a “low-value add for users, copy content from other websites or sites that are just not very useful.”

“At the same time, it will provide better rankings for high-quality sites—sites with original content and information such as research, in-depth reports, thoughtful analysis and so on,” they wrote.

Singhal and Cutts did not provide too many details about what this algorithmic change entailed; search engine ranking mechanisms are often closely guarded secrets. But they said this week’s change did not rely on changes it received from its “Personal Blocklist” Chrome extension. That tool, introduced last week, lets Chrome users eliminate Google search results from dubious domains. Google did, however, compare the Blocklist data it has gathered with the sites identified by the algorithm, and found that user preferences are “well represented” in the new algorithm.

“If you take the top several dozen or so most-blocked domains from the Chrome extension, then this algorithmic change addresses 84 percent of them, which is strong independent confirmation of the user benefits,” Singhal and Cutts wrote.

Google acknowledged that any change to its algorithm will affect the rankings of sites. “It has to be that some sites will go up and some will go down,” they wrote. “It is important for high-quality sites to be rewarded, and that’s exactly what this change does.”

Time will tell – to use a trite phrase – but, Google’s efforts to stem the flow of dross from the Web to our personal cpu’s is an useful step. There is little in the history of international commerce – especially media-driven commerce – to suggest that there are more than a very few individuals and companies willing to put quality above quantity.

Especially when the results of those decisions are measured in coin of the realm.