Did you know that Google hires humans as Search Quality Raters to rate the quality of websites?
Most people think quality is subjective. They believe that while quality is hard to define, you know it when you see it.
Not Google. Google has done a remarkable job of quantifying what they mean by High Quality relative to websites and web pages.
Most people who use Google are unaware of these people who (indirectly) help Google improve their search algorithm.
There are about 10,000 of these people world wide. They review webpages and rank them for quality, per strict criteria provided to them by Google.
This allows the Google engineers who work on the search algorithm to have a collection of sites that have been rated (by humans who are knowledgeable about the topic of the website) to use as a baseline while they work on the search algorithm.
If you work in SEO, or write for one or more websites, or are in any way involved in increasing the Google ranking of any websites, you owe it to yourself to read this document.
It is Google instructing their Search Quality Raters how to recognize what sites are of high quality and what sites are of low quality.
The collection of websites so rated is used as a resource by the Google search engineers as they update the Google search algorithm.
Below is a link to the most recent copy of this documentSEO Needs Link Building