We've been having an interesting debate over at SEOChat about "PR Bleed" and I thought I should blog a few of my ideas here. As everyone knows, inbound links are very important for ranking on a specific search term in Google. People talk about this loosely in terms of Pagerank (PR), juice and Search Engine Ranking Position (SERP). Many have pointed out that the correlation between PR and SERP is not as high as people once believed. This means that you can have a high PR site that does not rank well on a target keyword phrase. Likewise, you can have a very low PR site that ranks fantastically on a highly competitive keyword phrase.

As people try to understand how to deliver great SEO services to their customers, they ultimately come up against these concepts. Why? Because you need to understand them if you are going to advise a client on SEO. And one inevitable question emerges at some point: Do outbound links hurt my SERP? Unfortunately, this is not an easy one. Let's examine more closely.

I'm trained as an empirical scientist (about us), so I like to break things down into their equations. With a deep passion for technology, I also like to think about how the Internet manifests itself in databases. Your ranking in Google (SERP) for a specific search phase is essentially their final judgment on you. We all know that different pages on our website rank for different terms. This means that Google has developed a SERP score for every page on your website. Even more mind-boggling, this means that Google has a SERP score for every page on every website for every search phrase. With about 70 million active domains, and over ten billion active web pages, you can imagine that the combination is in the hundreds of trillions. But for any specific web page and any specific search phrase, there is a singe number. And Google uses these numbers (SERP scores) to rank order and show end-users the web pages that have the highest scores. This is SERP. And this is, therefore, SEO.

So back to the question of outbound links

As you consider the equation (or group of equations) that develop that single score for your web page on a specific search keyword, I can imagine three real possibilities when it comes to outbound links on that web page.

1) Outbound links are not considered at all. If this is true, the idea of PR bleeding is a myth. You need to stop worrying about PR bleed and link wherever you want as freely as possible. Some folks take this position and have even run some experiments to test the idea.

2) Outbound links are included in SERP scoring only as a blunt measure. In this scenario, the number of outbound links is included in the SERP score calculation as a quality measure to help keep bad web pages that exist only for the sake of linking out of the SERP. This seems extremely feasible. Google is in the business of showing end-users what is most appropriate. If Google has decided that, on average, single pages with hundreds of outbound links are usually not valuable to end-users, this type of rule is extremely logical. Under this scenario, the notion of PR bleed is actually true. In other words, adding more outbound links to your page will hurt the SERP, but only if you are over linking.

3) The quality of the outbound links are included in SERP scoring. In this scenario, PR bleed is not only true, but complicated. Whereas scenario 2 talked about counting the number of outbound links, in this scenario the quality and ranking of the sites that are LINKED TO is also included in the SERP score for a specific page on a specific keyword term. This bends your brain a bit, but supports the idea of "neighborhoods." You will often see people say that you should link to sites that are related to your business and rank highly. This scenario mathematically supports this idea.

Scenario 3 carries other connotations as well. While it supports the idea that PR Bleed is alive and kicking, it implies that you should not be worried about it. Why? Because any loss you will incur in SERP by including an outbound link will be offset be an increase due to the sites SERP (assuming you are linking to good stuff). So the conclusion here is that you should link out - but link carefully. And in the end, this is highly consistent with what Google tells us. It is very logical to think that they would favor sites that help users find other high-quality websites. In the end, this is what the Internet is really good at.