What is a quality website for a search engine?

How to define precisely the quality of a site and how search engines do they measure this quality?

The notion of quality of a website has become crucial for webmasters since that day of 24 February 2011 when the Panda Update was applied and 12% of sites are seen penalized for a question of quality. But what is quality from the point of view of a search engine?

Quality of a website or page by Google

A summary of the list given by Google to explain the Panda algorithm:

Actually we would like Google's results pages containing only these quality sites matching the description it gives!

How does Google know this is a quality site?

There is no absolute criterion for determining the quality of a thing. Longevity and efficiency criteria are commonly used in the real world, but it is difficult to apply them to a website. Different people expect different services and also tastes vary.

In fact Google evaluates quality of sites using a mathematical formula based on the ratio between the number of independent backlinks and the number of search queries that put a site in the results. (Ref USPTO Patent 8,682,892).

If a site is too well referenced and come often in results pages while it has few backlinks from completely independent sources, it is considered poor quality.

It is not related to design because content farms, the main targets of Panda, have a good design and are actually fun to visit. But their content is dull. These sites drain queries with keywords integrated in a banal text. This does not trigger backlinks.

See also: Quality of a website for a visitor. Design and overall building.