confuses a lot of webmasters and SEO Consultants. Another SEO asked me in the newsgroup alt.internet.search-engines why the site http://www.statcounter.com/ is PR10 despite having a lot of external links on the home page, basically why isn’t the leaked PR damaging the sites PR10 home page (the SEO consultant doesn’t believe PR leaks).
The SEO in question has misunderstood PageRank and how PR leaks from a site. Going to give a relatively simple explanation with what I hope is easy to understand maths.
How PR works
Every page has intrinsic PR, for ease of maths lets imagine every NEW page with no links to it has 1 PR point (not PR1, but an arbitrary unit we are calling PR points). This is intrinsic PR, our starting point for all those PR10 pages out there
When a page links to other pages it transfers** 85% (85% is the dampening factor from the original PR formula, might be more/less now, but doesn’t matter) of it’s PR points to the other pages it links to in a fair way.
**Transfers isn’t the right term as it suggest the original page looses PR, it doesn’t loose PR. You could imagine the “transfer” as creating PR points that is then transferred to the linked to pages, so the original page keeps it’s PR points.
If a page links to 17 pages each of those 17 pages receive 1/17th of the PR points available, in this case 1/17th of 85% of a single PR point equals 0.05 PR points.
Since the 17 pages also started with one PR point now they have 1.05 PR points each. These then link to other pages, transferring 85% of the total value they have accumulated from all links (so 85% of 1.05).
An important point though is once a page has PR it doesn’t loose it directly through links, as I said with the transfer note it’s more of a creation process. When a page links out (internal or external) 85% of it’s PR points are recreated/duplicated and they are shared equally to the linked pages. So it doesn’t matter if there is one link or 1,000 links from a page, 85% (it’s always 85% or whatever the dampening factor is now) of the total PR points of that page is recreated and then shared to all linked to pages. If it’s to one link that gets all 85% if 1,000 links each gets 1/1000th of 85%!!
Some people get confused at this point, they see an infinite creation of PR that they think would mean it’s easy to make PR10 pages. That’s why there is a dampening factor, every page has 1 PR point and 85% of it transfers to other pages through links. If you take the simplest scenario of 1 page linking to one other page-
–> = link to another page transferring 85% of the PR points.
1 PR point –> 0.85 PR points –> 0.7225 PR points –> 0.614125 PR points –> 0.52200625 PR points –> 0.4437053125 PR points
You can see the amount of PR points from the first page decreases (by 15%) as the chain of links increases. So the last page in the above chain has gained 0.4437053125 PR points that originated from the 1st page in the chain. As it happens move through ~15 links away from the original page and the recipient pages receive less than 1% of the first pages PR points. So the effects of a new page is limited due to the dampening factor.
The above ignores the intrinsic PR points the other pages had, if we add those you can see how PR accumulates-
1 PR point –> 1.85 PR points –> 2.5725 PR points –> 3.186625 PR points –> 3.70863125 PR points –> 4.1523365625 PR points
Remember this isn’t PR, it’s our PR points units the above linking system would still result in 7 PR0 pages, but the last page has more PR value than the previous 6 pages.
PR always goes up in the chain, never down so once a page has PR it can’t loose it through linking out. What linking out does is share the PR equally between all links.
The above link scheme is very simple, if we add just two links from the second to the last page in our chain (the page with 3.70863125 PR points) our final page that used to have 4.1523365625 PR points ‘looses’ PR points because the new pages gets a fair share-
1 PR point –> 1.85 PR points –> 2.5725 PR points –> 3.186625 PR points –> 3.70863125 PR points (links to 2 pages)
–> 2.57616828125 PR points (used to have 4.1523365625 PR points)
–> 2.57616828125 PR points (new page gains half the PR points).
And if it was three links-
–> 1.902877083 PR points (used to have 4.1523365625 PR points)
–> 1.902877083 PR points
–> 1.902877083 PR points
And if it was four links-
–> 1.788084140625 PR points (used to have 4.1523365625 PR points)
–> 1.788084140625 PR points
–> 1.788084140625 PR points
This is where leaking PR comes into play. Because PR points (PR) is spread equally through all links if we add new links to a page on our sites the original linked to pages gain less PR. Using the above examples if we had a home page with two internal links from it and we add two external links as well (4 links in total) you can see the two original internal links loose half the PR points they used to gain from the home page!!
This is leaking PR and doing something like this could be disastrous to a sites SERPs.
Fortunately it’s rare to have a home page with just two internal links, so the effects of adding external links is reduced. For example if we have a home page with 10 internal links they each receive 1/10th of the PR transferred from the home page. If we now add one external link the original 10 pages go from 1/10th of the PR to 1/11th since the new link receives a fair share.
How to Protect Your Sites PR
It should be obvious, think twice before linking to external sites. No external links means no lost or leaked PR.
Realistically you are going to link to external sites, so here’s a few tips to minimize the damage.
Avoid externally linking from the home page or your highest PR pages. Your home page will probably have the highest PR, if you can add no external links from it (unless to your own sites) this will protect the most PR possible.
Basically 10% of a PR6 page is worth a heck of a lot more than 90% of a PR3 page. If your home page is PR6 with 9 internal links from it and you add one external you’ve just leaked 10% of your PR6 link/PR benefit! If you have a PR3 links page with one internal link and 9 external links, you are leaking 90% of much less PR/link benefit.
So add external links to lower PR pages, give external sites less of your cake leaving more for you
You’ll note the PR is shared equally between all links, so if you increase the number of your links from a page it decrease the PR leaked to other sites. For example a site with 9 of your links and one external leaks 10% of the Pr/link benefit. Add 10 more of your links and now you leak 5% from that page, much better.
If you’ve looked into buying text links for PR you should keep an eye out for the above technique, you can find quite high PR pages selling text links, but they’ve really bulked up the number of internal links (I’ve seen over 150 on some sites!!) this means the buyer gets little link benefit from the link purchase!
rel=”nofollow” added to links tells the major search engines not to count this as a link. Useful for when you don’t want to use PR on a page, but don’t use it on your reciprocal link partners etc…, it’s not nice
When NOT to Protect PR
It’s difficult to prove conclusively, but I strongly believe Google will give a page a boost if it links to highly relevant pages, a lot of this boost will be due to the anchor text of the links, but I think some is due to the link destination as well. I’ve run tests on rel=”nofollow” and the anchor text of the links does count towards the pages SERPs, but I don’t know if by adding nofollow if it takes something away from the links.
So though it means sending PR to external sites I do advise linking out to relevant pages when it makes sense, it does help with rankings. Just try to avoid linking from the home page and other high PR pages.
