Pelland Blog

The Basics of PageRank: What Does It Measure & How Does It Work?

February 14th, 2009

There is a great deal of confusion about Google PageRank, one of the key – but optional – components of the Google Toolbar that you should have installed on each of your Web browsers. Pared down to the basics, PageRank is a numerical value, on a scale from 0 to 10, that indicates the importance of any page of content on the Web, based upon the concept that one page linking to another is essentially casting a “vote” for the importance of the second page. Not a truly democratic process, more “important” pages, based upon their own PageRank, carry more weight than pages that have been deemed to be less important, but the bottom line is that Google calculates each page’s relative importance from the “votes” that it has received. Certainly, anybody with even a rudimentary understanding of SEO (search engine optimization) can understand the importance of inbound links to a site.

You might ask, “Who cares?” You should! Those websites that you need to provide links to yours will often make their decisions based upon your the PageRank of your site’s Home page (or other linking page). Every webmaster would like to exchange links with a site with a PageRank of 7 or 8, but nobody wants to waste their time linking to a site with a PageRank of 1 or 2 (or even zero). More importantly, PageRank is an important factor in helping to determine a site’s ranking in the overall organic search results.

On the same token, you (or your webmaster) will want to take PageRank into consideration when you consider linking to other sites. Again, this is not a truly democratic process, and not all links are treated equally. For example, Google will filter out links from known link farms. Because incoming links from link farms are beyond any webmaster’s control (and link farms are more likely to try to capitalize upon a link to you if your site has a higher PageRank), Google will not penalize you for inbound links; however, you will be penalized for any outbound links to link farms or other penalized sites (often represented by a PageRank of zero).

What other factors come into play in determining the relative importance of one link versus another? For one, the number of links on a page. All else being equal, a link to your site from a page with only that one link is far more valuable than a link to your site from a page with 50 links. Basically, the more links on a page, the less PageRank value your page will receive from a link.

A few other points:

  • PageRank values are not arithmetic. Nobody outside of Google’s upper echelons knows the formulae, but it is generally agreed that the scale is logarithmic. In other words, it takes a lot more to advance from PR4 to PR5 than it takes to advance from PR1 to PR2.
  • A site’s total PageRank (the combined PageRanks of each of its component pages) is also an important measurement. More than anything else, this is determined by the number of unique pages within a site, clearly benefiting larger sites. New pages (“orphans”) should be directly linked to existing pages in order to yield any benefit for the PageRank of the overall site.
  • Links to pages with no outbound links of their own (or pages that Google has not indexed) are known as “dangling” links and have little or no value.
  • There are many experts who agree that outbound links that are not reciprocated can be a drain on a site’s total PageRank.

Because the Internet is constantly growing, the logarithmic scales that determine PageRank, by definition, must be continually evolving. This results in frequent changes in a page’s PageRank, where the measure will either increase or (more likely) decrease by a numerical value of 1 for no apparent reason, typically on a three-month basis. This phenomenon is referred to as the “Google dance” and is one more reason why it is important to continually build a site (by adding to its content) and to continually work on building the site’s number of inbound links from other highly-ranked sites.

Interesting tidbits:

  • According to Wikipedia, the name “PageRank” is a trademark of Google, and the PageRank process has been patented; however, the patent is assigned to Stanford University and not to Google. Google has exclusive license rights on the patent from Stanford University. The university received 1.8 million shares in Google in exchange for use of the patent – shares that were sold in 2005 for $336 million.
  • The name “PageRank” is derived from the name of its developer, Larry Page, one of the two founders, along with Sergey Brin, of what would become Google in 1998. The original search engine that Page and Brin developed as part of their research project at Stanford University in 1995 was called “Backrub”.

Learn more. The following references are listed in order of increasing complexity, ending with Page and Brin’s original research paper:

This post was written by Peter Pelland

4 Responses to “The Basics of PageRank: What Does It Measure & How Does It Work?”

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