Case Studies

SEO Case Study: Outbound Links

Posted by: Michael Gray, Jun 25, 2009

Supporting File

Actions:

Case Study Summary

Experiment: To determine if outbound links help a page rank for a term

Hypothesis: By linking out to other websites you improve your “hub score” and become a resource for a particular search term (see Hilltop algorithm).

Background: One of the questions that gets asked fairly frequently in search engine forums is do outbound links help you rank, and if they do what is the best way to structure the outbound links. Personally I’m a big believer in outbound links, not only do I support and endorse an interconnected web, but linking out helps you make friends. However the question is from a purely algorithmic standpoint do outbound link help or hurt you?...

Description:

Procedure: To test the experiment I created the following experimental pages.

    * a page with the search terms and filler copy (file 1)

    * a page with the search terms and filler copy the second search terms made up the anchor text for the outbound links (file 2)

    * a page with the search terms and filler copy “click here” made up the anchor copy for the outbound links (file 3)

    * a page with the search terms and filler copy the second search terms made up the anchor copy for the outbound links and were followed by a click here (file 4)

To allow you to see the results I published the files on this website. However to keep the experiment valid and free from “tampering” I repeated the experiment on two other websites, who’s URL’s I will keep secret (from this point forward known as control group 1 and control group 2). To keep the results as pure as possible I created 4 word phrase combinations which had no websites showing results. This proved to be more difficult than I anticipated as google is indexing dictionary pages from universities and other institutions (see Google SERPS giving broadmatch results). Here is a table of the results: (attachment)

From this test it appears that pages with no outbound links rank higher.

In all of the cases except one the pages using “click here” ranked higher than pages using the desired anchor text. Since the results for this test were not exactly what I anticipated I decided to give it another try comparing all of the factors at once.

While this testing is incomplete, there is a definite trend showing that linking out does not help a page rank for a particular term. Additionally in what seems very counterintuitive pages linking out using “click here” as anchor text rank higher than pages with the desired phrase as anchor text.

What does this mean from an SEO standpoint, well I wouldn’t be linking out from pages that you want to rank for a particular term. If you have to link out, use anything other than your desired keyword as the anchor text. However I wouldn’t start creating websites that are linking dead end’s, it would seem to easy to spot something like that programatically. I would however eliminate or keep to a minimum the number of outbound links on your “money pages”. Instead try placing the outbound links on secondary pages.

I would however like to see some other people repeat this experiment and compare the results, to see if they come to the same conclusions.