Google PR
The subject of Google PR is one that people seem to find endlessly fascinating.
PR stand for Page Rank and, at its simplest, Google PR is merely a measurment of
a page's 'perceived importance'. This perceived importance is fed into the overall
ranking algorithm (alongside relevance) to determine the final rankings within the
search results.
It's important to stress the 'perceived' word above. Google, nor anyone else for
that matter, can actually measure the quality of a page. What they do instead is
take note of user actions related to the site/page and infer the importance of the
content from those actions. For example, if multiple other sites decide to link to
a given page, Google infers that the content on that page must be of value.
Going a little further, suppose that two pages exist and that 10 sites link to
each page. Are they equally important? Not necessarily....Google digs a little deeper
and looks at the PR of each of the referring pages in order to determine how much value
each link should bestow. The more important the referrring page (the higher the PR) the
more importance Google places on the fact that they are recommending your page, and
the more PR is bestowed.
The details
Google PR is measured as an absolute value (0 -> infinity), but is converted to a
log scale (0 to 10) for publication.
The logorithmic scale means that it becomes increasingly difficult to
move up the scale as you progress.
It's believed that referring sites must themselves have a PR greater than a certain threshold value (4) in order to
be elligable to bestow PR upon sites they link to.
The PR boost bestowed by a link from a given page is inversely proportional to
the number of normalized (distinct) links on that page.
You can see your Google PR (or that of any web page) by installing the Google Toolbar.
Algorithm
Much web realestate has been devoted to equations and models hypothesizing the exact
PageRank algorithm. The truth is that no-one outside of google really knows. Page and Brin (the Google founders)
have themselves published slightly contradictory details. Having said that, the exact details are unimportant
(unless you happen to be a decitful person hoping to unethically manipulate your PR). For the rest of us, it's
enough to know that the general model looks something like this:
i.e more backlinks = good :)
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