Its easily said than done but google ranking analogy is one of the most complex analogy in terms of search engine optimization.
I came across a no. of resources which were both intresting as well a junk.
While this a ever changing calculation u rely only on guessing not only wild guessing but smart guessing. .This site has got avery decent pr but inspite of that it is not able to feature in terms of position.
Reasons are many but the valid ones i think are links and not any link but theme oriented links,keyword saturation and most importantly search engine placement.
Getting inbound links to your site is the only way to increase your site's average PR. How that PR is distributed amongst the pages on your site depends on the details of your internal linking and which of your pages are linked to.