On the forums or by email I am often asked the following sort of question: “How many Backlinks do I need to get in order to have PR5?”. The answer is simple and always the same one: “This question cannot be answered because the PR doesn’t only depend on the number of backlinks, it also and above all depends on the PR of each of those links…” Or to put it differently, a page can have PR5 with a single backlink whereas another one can have 3,000 backlinks and PR5 too.
How Do Backlinks Relate To PR? 
As a result it seems useless to carry out this type of analysis… Except if one is to compare the results in the long term. That’s what I have been doing over the past eight months by analysing tens of thousands of pages. For each data I get the number of backlinks and the PR of the page with those links. The data do not come from a tool using a Google Toolbar crack but from the “MyWri” tools on WebRankInfo which enables each WebRrankInfo member to instantly get the PR and the number of backlinks of 10 chosen sites (many other free SEO tools are also freely provided).
Results
The results are presented in the following table. For example the cell corresponding to column 5/2004 and row PR5 shows that in May 2004, an average of 104 backlinks was required to get a PR5. The number of sites analysed to get this figure appears on hovering over with the mouse (1044 measures in the given example). 
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Conclusions
I am busy preparing further studies on the subject and I hope to be able to share the results with you pretty soon. Please do get in touch if you wish to make suggestions.
Other studies
Another study that may be of some interest for you: Google test : hyphen and underscore.
More studies to come!
Olivier Duffez is an SEO consultant specialized on Google. Working on the Internet since 1997, he created in 2002 Web Rank Info, a free SEO resources French community (+13,000 members), and in 2003 his company Web Rank Expert. He created an online collaborative dictionary supported by Google.fr and DMOZ.
He’s giving SEO conferences in ImiTiki’s seminars and wrote a book about Google and SEO in 2004. He’s also part of the developpment team of PR Weaver and Agent Web Ranking softwares.
