I have always wondered about the parameters that Google must be taking into consideration in the calculation of the PR. Not only Google, but even Yahoo and MSN follow the same parameters in calculating PR of any site. That's the reason why the results in terms of PR never differs. One parameter is certainly the number of backlinks - dofollow ones certainly Other maybe the PR of sites from which a backlink is coming from. What are the others. Any ideas?
The PR of the referring site is obviously a big factor, as well as how many external links are present on that page. More external links means that that PR is divided out to more recipients. So if you had a choice between putting a single link of a PR5 page with 10 outbound links or a PR 5 page with 100 outbound links, you should pick the first option.