Google PageRank is an important concept  to understand if you are serious about being online.  Google makes the following statement about its search engine:

Traditional search engines rely heavily on how often a word appears on a web page. We use more than 200 signals, including our patented PageRank^TM algorithm, to examine the entire link structure of the web and determine which pages are most important. We then conduct hypertext-matching analysis to determine which pages are relevant to the specific search being conducted. By combining overall importance and query-specific relevance, we’re able to put the most relevant and reliable results first.

So what is the PageRank algorithm?  Fortunately, as Google notes, it is patented and we know what is in the patented algorithm. As an interesting aside, the "Page" refers to Google co-founder Larry Page and not a web page.

Google provides a definition of PageRank:

PageRank Technology: PageRank reflects our view of the importance of web pages by considering more than 500 million variables and 2 billion terms. Pages that we believe are important pages receive a higher PageRank and are more likely to appear at the top of the search results. PageRank also considers the importance of each page that casts a vote, as votes from some pages are considered to have greater value, thus giving the linked page greater value.

For the mathematically minded, the original algorithm is:

PR(A) = (1-d) + d(PR(t1)/C(t1) + … + PR(tn)/C(tn))

PR = PageRank (A) = for a webpage called A

d = a damping factor (usually set at 0.85)

t1-tn = the PageRank for every webpage that links to page A

C = the number of outbound links each page t1, t2, t3 …..tn that links to page A

For the mathematically challenged , this can be boiled down to:

A page’s PageRank = 0.15 + 0.85 x (the percentage entitlement of every page that links to page A); 

where the percentage entitlement is determined by the number of outbound links on every page.

So every page starts with a PageRank of at least 0.15 (woohoo) but then collects votes from sites that refer internet users to it. Unfortunately PageRank goes from 0 to 10, so 0.15 is a pretty slow start. The damping factor at 0.85 is to account for the fact that eventually a searcher will stop clicking on links.

It is clear that getting links from webpages with a higher PageRank than your site assists in increasing the PageRank of your site. And as Google states above "pages that …. receive a higher PageRank … are more likely to appear at the top of the search results".

A couple of interesting points to note here:

• Google does make changes to its algorithm over time;

• The patented algorithm does not explain everything (e.g. is the scaling of PageRank from 0 to 10 a straight-line or logarithmic scale);

• The more outbound links a site has, the "less" PageRank it has to give to your site;

• Links from high PageRank sites, all things being equal, will benefit your site more than lower ranked sites

So you can see why people bang on about offpage SEO. We know Google uses PageRank, we know the algorithm that drives it, and it is about links from other sites. But, and it is a big but, Google makes it quite clear that a raft of other variables go into determining the ranking on a search engine result page.

So, yes inbound links are very important, but not to the total detriment of other SEO.

Marshall and Gary