There are so many factors. Like, how many out going links that page has, quality of the page and the niche of the page.
Any proof ? I'm sure you don't have any .. don't believe every single word a serach engine tells you .. Relevancy isn't even defined .. do you know what's relevancy? do you know how google determine the subject of a web page ? try the adword keywords tool and test your website .. you will be surprised ... @Lucky_romania : that grid is tooooooo old, believe me .. there are so many other factors nowadays ..
It's quite simple. Here's the math: PR 5' + PR4's divided by PR 6's X Pi = 95.76545 Example: 586 PR 5's + 120 PR 4's divided by 22 PR 6's mutiplied by Pi (3.14...) minus 95.76545 In this example, the PR = 5 Easy enough?
Works!! until now. I tell you that you need about ~20 backlinks from PR5(related) to bring your site to PR5