This is a fourth part of a five-part series on SEO factors for ranking your web site well in the search engine results pages (SERPs). In this article we talk about the URL of the page, link authority, PR, outbound links, number of outbound links and more.
Domain Authority Factors
There are several measurements of domain authority from the perspective of links: the QUALITY of links pointing to a domain, the QUANTITY of links, toolbar pagerank, domain rankings on search results and domain keyword relevance to the topic. Let's look at how each can affect the value of a link to your website:
How quality of links that point to a domain affect a link that is pointed to your website. Example: www.site1.com links to you. How is a link from www.site1.com to your site affected by other links that point to www.site1.com?
Trusted links to a domain that links to your site are very important. If domain X has 100 trusted links, then a link from X is more valuable than a link from Z that has 1000 trashy links. This is especially true for new websites, which have low trust profile and tend to sit in the supplemental index.
How quantity of links to a domain affect a link coming from that domain to your website. Example: www.site1.com links to you. How is a link from www.site1.com to your site affected purely by the number of outside links that point to www.site1.com?
This depends in part on the quality of outside links. For example, if X has 1000 links and Y has 100 links, then a link from X is more valuable -- if all of those links are of equal quality. If W has 1000 trashy links and Z has 50 quality links, then a link from Z is more valuable.
The game is about quality. Though paid directories still tend to work, their value is going down. I believe Google will soon completely eliminate their effect, or minimize it so much that it simply wouldn't be worth pursuing.
How Toolbar pagerank of a domain affects a link coming from that domain. Example: www.site1.com has PR 4. How does that affect a link that comes from www.site1.com to your website?
Toolbar pagerank is not a real measure of Google pagerank. We know that it's delayed for at least three months and can be adjusted by Google without real effects on search rankings. Do not trust pagerank too much; focus on link analysis instead. It's a good general measure, but Google may be skewing it to offset link buys.
How domain rankings on search results affect a link coming from that domain to your site. Example: site1.com rank #4 for "widgets." How valuable is the link to your website, which you want to rank for "widgets" or "purple widget"?
This factor is very influential. A domain ranking for your keyword has been determined by algorithms to be very valuable and worthwhile. If you want to rank for the same or similar terms, then a link from that domain is an influential vote.
Example 2: site1.com ranks #2 for "purple cow." How valuable is the link from www.site1.com to your domain, which you want to rank for "purple widget"?
This is influential as long as the linking domain has high trust and authority. Topically unrelated links coming from trusted websites still pass ranking value. They indicate a vote by a linking website, and since the website is trusted, that trust is partially passed on to you.
How does relevance of keywords within linking domain name affect your site? Example: www.widgets.com links to your site. How does that affect the link's value if you want to rank for "purple wigets"?
There a lot of disagreement about this. It is a fact that many domains can rank for keywords completely unrelated to their name. Perfect examples are Wikipedia and About.com. Domain keyword relevance can help, but it is not the deciding factor. Website authority and trust far outweigh this value.
Search Optimization 
