Site Authority is gained over time, and is a lot harder to get than PageRank is – the authority of a site somehow effects the ranking of its pages, and it also effects the tolerance that search engines show towards the site.
Not much is known for sure about the Authority rank, but it is pretty obvious that search engines treat some sites different than others.
Older "Authority" sites will often have new pages indexed, and well ranking, far easier than younger sites. Younger sites may even get out-ranked by these older sites.
What effects a sites Authority?
There are areas of SEO that constantly change, and this is one of them. So it is hard to say anything specific about Site Authority. Some experts may be able to get a "feel" about certain things effecting it, but mentioning those here seem pointless – they could be outdated tomorrow! It is also one of the things talked less about, since it will slowly build on its own over time.
Some of the things assumed to have a effect on site authority, as of the writing of this Reference, would be:
- Content length
- Keywords and Keyphrases found throughout the site
- Keywords in Anchor Text
PageRank is not thought to have any direct effect, but it can effect indexing and ranking of new pages – if the new pages are linked to, from a page with high PageRank.