Google has been under increasing pressure in recent months to improve its search results. From accusations of SEO gaming by big sites to a search results page dominated by the likes of Demand Media and other content farms, the search engine has repeatedly heard the cry that it was becoming less and less relevant. Most recently, the company launched an extension to allow users to block results from certain domains.

Today, Google announced that it had made a "big algorithmic improvement" that, unlike other changes, could be noticeable to its users.

Google Fellow Amit Singhal and Principal Engineer Matt Cutts announced the changes this evening, noting that the improvement happened without the help of last week's toolbar release:

Many of the changes we make are so subtle that very few people notice them. But in the last day or so we launched a pretty big algorithmic improvement to our ranking--a change that noticeably impacts 11.8% of our queries--and we wanted to let people know what's going on. This update is designed to reduce rankings for low-quality sites--sites which are 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.

We can't make a major improvement without affecting rankings for many sites. It has to be that some sites will go up and some will go down. Google depends on the high-quality content created by wonderful websites around the world, and we do have a responsibility to encourage a healthy web ecosystem. Therefore, it is important for high-quality sites to be rewarded, and that's exactly what this change does.

While the changes may have been made without input from the extension, Google notes that "this algorithmic change addresses 84% of them, which is strong independent confirmation of the user benefits."

The changes will take place initially in the U.S. and roll out in other locations over time.