Saturday, 4 February 2012

The PageRank Equation

Here is the official PageRank equation. It is calculated by solving an equation that
includes each of the billions of web pages in the Google index:

PR(your page) = 0.15 + 0.85 [(PR(page A) / total links (page A) ) + (PR(page B) / total links (page B) ) + …]

A couple of observations to note about the PR equation:

•   PR is based on individual web pages – not on a website as a whole.

•   The PR of each page that links to your site in turn is dependent on the PR of the
    pages that link to it, and so on iteratively.

•   A link’s value (amount of PageRank or “voting power” forwarded to the linked-to
    page) is at most only 85% of the linking page’s PageRank value, and this value is
    diluted (decreased) by the number of other links on that page.

•   PR has nothing to do with keywords or text in links - it is purely dependent on link
    quantity and link strength, as discussed previously.

Some may incorrectly conclude that a link from a page with a PR = 4 and with only a
few outgoing links is worth a more than a link from a page with a PR = 6 with 100
outgoing links because for the latter, the “voting power” or value is divided up among
99 other links.

However, you must remember the logarithmic nature of actual PageRank. A link from
a PR = 6 page with lots of outbound links may indeed be worth more than a link from
a PR = 4 page that has only a few outbound links.

The Evolution of PageRank
Pagerank used to be a simple weighting factor for all links regardless of the topic of
the page that contained the link. This led to a small industry that focused around
buying and selling high-PageRank links. However, when anyone can achieve high
rankings by simply buying enough links from any website, or trading links with any
unrelated website, Pagerank loses its value as a factor in ranking websites
As such, Google has done some tweaking of how it analyzes the value of links. Links
are now scored differently and some links may not count as much as they used to.
PageRank as the defining metric for links is becoming less important and the other
variations listed below are becoming more important.

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