Monday, November 29, 2004

The Impact of Outbound Links on Page Rank

If you have been following any of my "Power Linking" exploits you will know that I have recently been writing articles and creating content-rich pages and placing them strategically on as many sites as I can. Some of these are "article" sites, some of them are blog sites, and some of them are my own sites spread around on a variety of different hosts.

Regardless of where the content is placed, one of the questions that constantly comes up is "How many links should I plant in these pages?"

Let's say I want to write an article focusing on a specific product -- for instance, "Business Card Displays" -- in order to (among other things) increase the number of links pointing to the home page of the client's website ( Should I restrict myself to planting one embedded link pointing back to the home page? Or should I embed a number of other links as well, pointing to various other pages on the site? Quite a few SEO "experts" seem to think that the impact of a link is watered down by the total number of other links on that page, and, therefore presumably, that the impact of a link pointing from a specific page to your "target" page would be much more significant if it was one of only a few on the page.

I finally got around to doing a bit of research into this question.

The "PR Leak" position is stated very clearly in an article by Phil Craven called Outbound Links". Craven says:

"Outbound links are a drain on a site's total PageRank. They leak PageRank. To counter the drain, try to ensure that the links are reciprocated. Because of the PageRank of the pages at each end of an external link, and the number of links out from those pages, reciprocal links can gain or lose PageRank. You need to take care when choosing where to exchange links."

Craven is claiming that not only will your outbound links have a negative impact on the PR of the page containing them, but the outbound links of the pages linked to will drain PR away from your page as well. We might call this "second order PR Leak". He goes so far as to suggest that you should disguise outbound links with javascript.

Unfortunately he offers no theoretical or statistical evidence to support the "PR Leak" position.

Coming down on the other side of the debate is article by Jon Ricerca called Does the Number of Links on a Page Affect Its Ranking?. Jon Ricerca concludes: "...the results are very conclusive. Google ranks pages with outbound links much higher than pages without links. The SEOs touting the ‘PR Leak’ theory are simply wrong."

Ricerca's starting point is that the PR Leak theory is simply a theory -- pure speculation -- and therefore it needs statistical data to be either confirmed or denied. The statistical data he offers is based on a relatively limited number of sites, and a relatively limited number of searches (see his data and disclaimers).

The assumption he makes is that if the "PR Leak" theory were correct, then for any given keyword a significant number of high ranking sites would have fewer outbound links than the sites lower down in the rankings. The lower ranking sites would presumably have been negatively affected by their outbound links. But he finds exactly the opposite to be the case. All of the higher ranking sites have more outbound links than the lower ranked ones!

This is all very interesting, and is certainly pretty convincing evidence against the PR Leak theory.

Unfortunately, this is not exactly what I set out to determine. This shows that outbound links do not adversely affect the PR of the page that contains them. But I really started out wondering about the impact of links on the target page. After all, this is the point of "power linking" strategies -- to enhance the ranking of the target pages. So it is important to know if a link from a page with one outbound link is given more weight than a link from a page with numerous outbound links.

My Google searches did not turn up any useful answers to this question. Indeed, it is difficult to see how a study could be set up to answer this question. Any fairly simple study would have to make some pretty serious assumptions.

In fact, I may have some of the relevant data available to me on my own sites. I could begin by finding pairs of pages within the same site, both of which are linked to a specific page in another site. The first page in the pair will have lots of outbound links, and the second page will have considerably fewer. Then all I have to do is see which of these pages in any given pair is reported in the "backlinks" for the target page more often.

If the page with fewer outbound links is reported more often, then that supports the conclusion that outbound links from pages with fewer links are more valuable (have a greater -- or at least more consistent -- impact on the target page.) If there is no difference in the frequency of reportings, then that suggests that there is no significant difference.

I will try to compile some of this data over the next couple of days, and will report back...


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