fred9989 - 12:17 pm on Jun 19, 2006 (gmt 0)

Authority surely implies reliability: good, solid, factual information on as comprehensive a range of topics about a subject as possible.
That might reflect the authority of someone with personal experience in the field, who is reporting in an unbiased, unprejudiced way the facts of the matter, or it might mean an expert from government, academia or the community at large.
Criteria include depth of thinking, breadth of knowledge, accuracy of facts, and respect from peers.
The problem in assessing this kind of site through metrics is that it is likely to be much less popular than a more trivial site, even when the issues it deals with affect a large number of people.
(Think of the UK tabloid press vs the UK broadsheet press. This makes it clear authority may not mean popular. What can be popular is trivial inaccurate flim flam that diverts and entertains a lot of people.)

Quality might imply a different set of criteria: well designed information provision, set out in a way that appeals to many people. The Daily Mail, IMO one of the most prejudiced, biggoted and hypocritical newspapers in the UK, is arguably also one of the most high quality - and it has an extremely high readership. It gives people what they want, not necessarily what they really need.
Now, imagine two websites reflecting those chacteristics about the same subject. How would you assess the significance of these websites, and how would you design a single system that presents both of them in the top results for a search query?
Rod