You know search engines evaluate a site based primarily on the links going to it (inbound links). The PageRank of the sites on which the inbound links are located, and the anchor text of the links, matter a lot. But if you're like most webmasters, you don't appreciate the value of outbound links.

Outbound Link Relevance & Anchor Text

The clearest way that outbound links can affect SEO is through their anchor text.

Outbound links' anchor text affects a page's search engine ranking in much the same way that inbound links' anchor text affects search engine ranking. Anchor text of inbound links is arguably the most important factor in search engine rankings for particular keywords. For instance, if "fuzzy keyword" is in the anchor text of a link to a webpage, that webpage may well appear in SERPs for "fuzzy keyword" even if neither the word "fuzzy" nor "keyword" appears anywhere on your site.

Outbound links' anchor text works the same way, though it is slightly less powerful. If you have a particular keyword in the anchor text of a link on a webpage, that webpage will likely show up in search engine results--even if it appears nowhere else on the page, and even if there are no inbound links with that anchor text.

Don't believe me? Look at your web traffic logs. Check out the search engine traffic to specific pages. You'll likely see plenty of instances of the page getting traffic for search strings that appear nowhere else on the page but in the anchor text of outbound links.

One example from a site I own is on endometrialcancer.org, a project devoted to provided information about a disease. There are separate pages for symptoms, diagnosis, prognosis, and other aspects of the disease. Strikingly, one page my rank highly for another page's target keyword, if it links to the other page with the target keyword in its anchor text. For instance, the "diagnosis" page may outrank the "symptoms" page for the keyword "endometrial cancer symptoms," merely because the "diagnosis" page has that keyword in the anchor text of its link to the symptoms page.

How to shoot yourself in the foot with outbound link anchor text relevance:

There are four main ways to shoot yourself in the foot by mishandling outbound links' anchor text:

• Don't include relevant outbound links on the webpage. There are many sites nearly all of whose pages have no outbound links but a standard navigation bar, and perhaps a link to the site's web designer, host, or CMS maker. What exactly is a search engine algorithm supposed to make of a webpage if the only outbound links it has have anchor text such as "about us," "contact," "privacy," "site map," "Design by TechGnome," and "This site powered by Mambo Open CMS"?

• Don't include off-site outbound links on the webpage. Think about it for a moment: what is the one thing a truly informative webpage would have to have, besides content? Links to other sites! If a page has no outbound links to other sites, there is a good chance the page is a dead end, or worse, a billboard. At the very least, include at least one intra-site link that isn't part of the standard site navigation.

• Include irrelevant links. I have a client site that sells computer equipment. After paying me all the money for my services largely in hopes of getting more search engine traffic, they decide to sell irrelevant links on the homepage, for a fraction of what they paid me. If you were a search engine algorithm, what would you make of a site that had "computer equipment" in the page title, headings, and inbound link anchor text--but had two outbound links with "Costa Rican beach resort" and "Low-cost mortgages" in the anchor text? If I were the algorithm, I'd get a little confused, and play it safe by ranking the site for none of those keywords. After all, there are plenty of sites that make a less ambiguous case for their relevance for any of those keywords.

• Include relevant outbound links, but forget the anchor text. If you are linking to a relevant webpage, whether on-site or off-site, by all means, use your page's target keyword in the anchor text! Now is not the time to get lazy and use the URL as the anchor text. You are doing the right thing by linking to relevant webpage. Make sure you get credit for your good deed!

After all, they call it the web because the links go both in and out, tying sites together like nodes of spider silk. If links were only meant to flow one way, they'd just call it the chain.

Don't chain your website down. Start sharing the links.