PageRank sculpting is the process of attempting to direct the way that PageRank flows within (and into and out of), your website. PageRank is a link analysis algorithm named after Google co-founder Larry Page, that assigns a numerical rank (from 0 to 10) to each element of a hyper-linked group of documents, to measure its importance within the group.
According to Google’s Matt Cutts, the most popular way of looking at PageRank is as a flow that happens between documents (or pages) across outbound links. However, he cautions that it is not a strictly accurate analogy.
PageRank Decay & The Infinite Loop
Very simply, (very very simply), the way PageRank works is as follows: If a page has a PR of 5, and contains 2 outbound links, it passes a PR of 2.5 to each page that it is linked to. If there are 5 outbound links, then each page receives a PR of 1 from the original page.
Because of the risk that pages linked together in a loop, (where the final page was linked back to the first page), and it’s potential to generate an infinite PageRank, Google introduced a decay factor into the transfer of PageRank, where a percentage of rank is lost, before it is redirected into the next page.
PageRank and Nofollow Links
The “rel=nofollow” attribute was first introduced in 2005, and is supported by most search engines. It gave webmasters the ability to tell search engines that the appearance of a given link did not mean that the webmaster necessarily supported or condoned it. When it comes to Google for example, adding the nofollow attribute to a link tells Google not to pass any PageRank on to the site the link points to.
When it comes to applying the concept of passing PageRank on pages with both normal and nofollow links, in his blog post about PageRank Sculpting, Matt Cutts had the following to say,:
“So what happens when you have a page with “ten PageRank points” and ten outgoing links, and five of those links are nofollowed? Let’s leave aside the decay factor to focus on the core part of the question. Originally, the five links without nofollow would have flowed two points of PageRank each (in essence, the nofollowed links didn’t count toward the denominator when dividing PageRank by the outdegree of the page). More than a year ago, Google changed how the PageRank flows, so that the five links without nofollow would flow one point of PageRank each."
So the nofollow attribute not only tells Google not to pass PageRank, but it tells it not to count the link as an outbound one from the page.
As we explained in the first paragraph, PageRank sculpting involves attempting to control the PageRank of specific pages, by using things like the nofollow attribute to direct the flow of PageRank. However, in the same blog post, Matt Cutts says that he doesn’t recommend such sculpting.
“I wouldn’t recommend it, because it isn’t the most effective way to utilize your PageRank. In general, I would let PageRank flow freely within your site. The notion of “PageRank sculpting” has always been a second- or third-order recommendation for us. I would recommend the first-order things to pay attention to are 1) making great content that will attract links in the first place, and 2) choosing a site architecture that makes your site usable/crawlable for humans and search engines alike…
…There may be a miniscule number of pages (such as links to a shopping cart or to a login page) that I might add nofollow on, just because those pages are different for every user and they aren’t that helpful to show up in search engines. But in general, I wouldn’t recommend PageRank sculpting."
In the same vein, he added that hoarding PageRank by giving all your outbound links the nofollow attribute isn’t the best idea either.
“In the same way that Google trusts sites less when they link to spammy sites or bad neighborhoods, parts of our system encourage links to good sites.”
As always, Google recommends that the best way to improve your site is to create relevant, high-quality content that encourages inbound links, and not to pay too much attention to the way that Google’s algorithms work. Not only are these highly confidential, but they’re also subject to regular change, thanks to people’s attempts to outguess them.
However, he does conclude by saying that although the algorithm they uses changes, he’s pretty sure that this aspect of it won’t. No guarantees though.