Link Value: It's Not What You Think
When Google first introduced Page Rank (PR) as a way of determining the value of websites, PR was calculated according to the number of inbound links that a given website possessed. In essence, the greater the number of inbound links on a website, the higher the PR that was assigned to it. Link popularity became one of the key parameters by which Google, as well as other search engines, calculated a website's importance. As a website's importance grew, the likelihood of it being placed at the top of the search engine results pages (SERPs) similarly increased.
Because PR value is calculated on a logarithmic scale of 0-10 using a published algorithm (1), user techniques for achieving high PR quickly developed. The practice of reciprocal and three-way link-swapping enabled many websites to attain a PR of 2 or 3 in a matter of days. "Link farms", where website owners could pay for one-way inbound links from several hundred to even thousand low PR or spam sites, as well as FFA (free for all) link sites, enabled websites to shoot to the top of the SERPs almost overnight. Other website owners sought to increase their website's PR by employing more legitimate linking strategies, including article marketing, posting comments on relevant blogs, developing forum signatures that included their website address, and submitting URLs to website directories. Posting quality content also increased a website's PR because other users perceived its content as a resource to which they could link.
Because many website owners were participating in link schemes (2) to achieve a higher ranking with Google and other search engines, search engines combated this practice by either disqualifying the spam sites or by "sandboxing" the offending websites. However, in the case of legitimate linking strategies, calculating the PRs of those websites became a challenge. For example, how do you determine if your website's PR value is improved more through several links to its home page from three PR5 websites or 1 link to its internal page from a PR7 website? Likewise, do high PR site links still raise your website's PR value if they are mixed in with low PR and/or spam links?
10 tips for understanding link PR
The following 10 tips help illustrate how link value is determined not only by several factors including page placement, use of keywords, text/image origin and page seed set position. Alternately, link value can be reduced by incoming links from spam, adult sites, or low PR sites. This information can help you determine how to use and place incoming links to their utmost advantage, as well as to avoid those links that can actually lower your site's PR.
1. Place your incoming links higher. With all other variables being considered equal, a link that is placed higher in the HTML body code of a page is likely to be ranked higher than if the same link is placed lower in the code. The reasoning behind this ranking is largely based on user behavior; web users are more likely to click on the first link they see before becoming bored and clicking on a random page (3). Therefore, if you have a high PR inbound link to place on your page, don't reduce its weight by including it within the last paragraphs of your content; place it as far up on your web page as possible for maximum effect. Additionally, emphasize this link's prominence by changing its font, size, or even its color.
2. Favor inbound links from sites with few outbound links. Search engines may place greater weight on links that originate from sites that have fewer outbound links versus those sporting hundreds of outbound links (4). This is something to consider when you are sending out queries to high PR websites that may already possess thousands of outbound links. In some cases, it may be more productive (and easy) to target lower PR websites for the simple reason that they will probably also have fewer outbound links.
3. Choose links that are closer to a "seed" set. According to Pavel Dmitriev of Yahoo!, seeds are documents that are "used as a starting point for the crawling" of search engine bots and "may influence how many documents of a particular host are crawled (5)". Therefore, links that are themselves just a few clicks away from a seed site (i.e., Library of Congress) are more likely to be crawled and indexed. As a result, a link located closer to a seed site is likely to be given a higher value.
4. Place image alt text, not link titles, inside images. A common SEO technique involves adding relevant link titles inside of web images. However, if the image is not viewable, the image alt (i.e., alternative information) text, but not the link title, can still be displayed in its stead. In addition, when the image is inside a link, the alt text can function as the anchor of the link whereas the title, once again, does not. As a result, image alt text will result in higher PR than just a link title inside the image (6).
5. Unpopular page links trump the popular if those links originate from trusted sites. A link originating from an unpopular or unimportant page of a trusted site (i.e., cnn.com) can be assigned more value than a link originating from the homepage of an untrusted site. Part of this valuation discrimination has to do with search engines avoiding possible spam sites; as a result, even legitimate links coming from unknown and therefore untrusted sources may not receive due credit.
6. Analyze how users define your site by their links. Search engines assign value to incoming links by their keyword relevancy to your site. Web users might be linking to your website but using different search terms than expected, resulting in a lower PR value being assigned to those links. By analyzing the incoming links on your site, you may find that many of them originate from unrelated subject material. If this is the case, it can lead to search engines discrediting the value of those links. Finding the reason why unrelated sites are linking to your site, and either removing them or accommodating their content, can help resolve this issue.
7. Affiliate/redirect links are not given a high PR value. In many cases, links from what appear to be authority sites are managed through their affiliate sites, not the authority sites themselves. Case in point is CNN, which has numerous online affiliate sites such as cnn.com/LOCAL. While a link from an affiliate site has merit, it does not compare to the value assigned to the authority site itself.
8. Spam links can depreciate the value of high PR links. Even if your website contains many links that are of high PR, the value of those links can be lowered if your website is also being linked to via spam, adult sites and overly commercial sites (e.g., sites with excessive PPC, banner and contextual ads). Oftentimes, the low PR culprit is comment spam, which is hard to catch even with the best filters.
9. Reciprocity often lowers a link's PR value. When several link analysis experts were asked whether reciprocal links are as valuable as one-way inbound links, most agreed that reciprocity, while useful to an extent, lowers a link's overall value (7). In essence, your website carries a higher PR if it is viewed as being more "in demand" than "demanding".
10. Links from different sites beat many links from the same site. Even if a site has a high PR value and links to your site several times, those extra links may not enhance your own site's PR beyond what was reached with the initial link. This is because search engines favor link diversity over number when assigning value to a site (8). As a consequence, you benefit more from having a few unique links from different and lower PR sites than many links from even the same very high PR site (9).
Brin, S.; Page, L. (1998). "The anatomy of a large-scale hypertextual Web search engine". Computer Networks and ISDN Systems 30: 107–117.
Link schemes. http://www.google.com/support/webmasters/bin/answer.py?answer=66356
Google's Reasonable Surfer: How the Value of a Link May Differ Based upon Link and Document Features and User Data. http://www.seobythesea.com/2010/05/googles-reasonable-surfer-how-the-value-of-a-link-may-differ-based-upon-link-and-document-features-and-user-data/
How Search Engines Use Link Analysis http://searchenginewatch.com/article/2064732/How-Search-Engines-Use-Link-Analysis
Host-based seed selection algorithm for Web crawlers. http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=1&p=1&f=G&l=50&d=PG01&S1=20100114858.PGNR.&OS=dn/20100114858&RS=DN/20100114858
Testing image links with ALT tags and titles http://wac.osu.edu/tutorials/links-testing.htm
Link value factors. http://wiep.net/link-value-factors/
Day 13: Is PageRank Important? http://www.seobook.com/learn-seo/is-pagerank-important.php
All Links are Not Created Equal: 10 Illustrations on Search Engines' Valuation of Links http://www.seomoz.org/blog/10-illustrations-on-search-engines-valuation-of-links