PageRank is the algorithm used by the Google search engine, originally formulated by Sergey Brin and Larry Page in their paper The Anatomy of a Large-Scale Hypertextual Web Search Engine. It is based on the premise, prevalent in academia, that the importance of a research paper can be judged by the number of citations the paper has from other research papers. Brin and Page have simply transferred this premise to its web equivalent: the importance of a web page can be judged by the number of hyperlinks pointing to it from other web pages.
So what is the algorithm?
It may look daunting to non-mathematicians, but the PageRank algorithm is in fact elegantly simple and is calculated as follows:
PR(A) = (1-d) + d (PR(T1)/C(T1) + ... + PR(Tn)/C(Tn))
where PR(A) is the PageRank of a page A
PR(T1) is the PageRank of a page T1
C(T1) is the number of outgoing links from the page T1
d is a damping factor in the range 0 < d < 1, usually set to 0.85 The PageRank of a web page is therefore calculated as a sum of the PageRanks of all pages linking to it (its incoming links), divided by the number of links on each of those pages (its outgoing links).
And what does this mean?
From a search marketing or search engine optimisation point of view, this means there are two ways in which PageRank can affect the position of your page on Google: -The number of incoming links. Obviously the more of these the better. But there is another thing the algorithm tells us: no incoming link can have a negative effect on the PageRank of the page it points at. At worst it can simply have no effect at all.
-The number of outgoing links on the page which points at your page. The fewer of these the better. This is interesting: it means given two pages of equal PageRank linking to you, one with 5 outgoing links and the other with 10, you will get twice the increase in PageRank from the page with only 5 outgoing links. So, when considering your search engine optimisation approach, remember that Google doesn't just rank by keyword, it ranks by links. |
