First thing to realise is that “page rank” (i.e. your page’s ranking in the SERPS) is NOT PageRank!
PageRank™ is a link analysis algorithm, named after Larry Page (Google’s co-founder), used by Google. PageRank was developed at Stanford University by Larry Page and later Sergey Brin as part of a research project about a new kind of search engine. The project started in 1995 and led to a functional prototype, named Google, in 1998. Shortly after, Page and Brin founded Google Inc. While just one of many factors which determine the ranking of Google search results, PageRank continues to provide the basis for all of Google’s web search tools.
Most people will come across PageRank either by installing the Google toolbar or by being told what their PageRank is by someone trying to sell SEO services. It will usually be expressed as an number out of ten eg. 3/10. In reality this is not very accurate; this toolbar PR is only updated a few times a year and is only meant as an “indicator” of your true PR. Google has not disclosed the precise method for determining a Toolbar PageRank value.
Another version of PR can be found in the Google directory (http://www.google.com/dirhp?hl=en) these listing come direct from DMOZ but Google lists them in order of PR. This is a separate PR from that of the Google toolbar The Google Directory PageRank is an 8-unit measurement, Google Directory does not show the PageRank as a numeric value but only as a green bar – here is what Google says about it:
The green ratings bars are Google’s assessment of the importance of a web page, as determined by Google’s patented PageRank technology and other factors. These PageRank bars tell you at a glance whether Google considers a page to be a high-quality site worth checking out.
This is also a “representative” PR and is not the real PR.
So… What is PageRank?
Well here is how Google describes it:
PageRank relies on the uniquely democratic nature of the web by using its vast link structure as an indicator of an individual page’s value. In essence, Google interprets a link from page A to page B as a vote, by page A, for page B. But, Google looks at more than the sheer volume of votes, or links a page receives; it also analyzes the page that casts the vote. Votes cast by pages that are themselves “important” weigh more heavily and help to make other pages “important”.
Actual page rank is expressed as a number between 0 and 1 and is relative to all other pages on the internet, thus it is constantly changing as more pages are added to Google’s index. It can also be seen as the probability that a web user following random links will eventually end up a specific page.
In short, the number of in-links to a page is important but then so is the PR of the page doing the linking. Also the anchor text in the link plays a part as does the overall content themes of the page the link is on. Google looks at other factors such as domains, countries, IP addresses etc.
Put all this together what do you get?
Multiple, keyword-rich links from lots of popular web sites that follow similar themes and are not on the same domain or server as your pages are gold dust. If you can get these links, then good PR will follow.
To PR or Not to PR
However, there is a very strong argument that Google should ditch all visible representations of PR as it is distracting site owners and marketers from what really counts – Content! If your site has good, well written, keyword rich, interesting content then users will visit, sites will link and rankings will increase. Being fixated with how many links you have can detract from the real point.
For anyone who is interested in science behind PageRank you can read this wiki article http://en.wikipedia.org/wiki/PageRank.