How Does Links Influence Search Engine Rankings
The concept of using links as a way to measure a site’s importance was first made popular by Google with the implementation of its PageRank algorithm about it, but Google’s rapidly increasing user base popularized it. In simple terms, each link to a web page is a vote for that page, and the page with the most votes wins.
The key to this concept is the notion that links represent an “editorial endorsement” of a web document. Search engines rely heavily on editorial votes. However, as publishers learned about the power of links, some publishers started to manipulate links through a variety of methods.
This created situations in which the intent of the link was not editorial in nature, and led to many algorithm enhancements, which we will discuss in this chapter. To help you understand the origins of link algorithms, the underlying logic of which is still in force today, let’s take a look at the original PageRank algorithm in detail.
The Original PageRank Algorithm
The PageRank algorithm was built on the basis of the original PageRank thesis authored by Sergey Brin and Larry Page while they were undergraduates at Stanford University. In the simplest terms, the paper states that each link to a web page is a vote for that page. However, votes do not have equal weight. So that you can better understand how this works, we’ll explain the search engine rankings algorithm at a high level. Pages can then increase their PageRank by receiving links from other pages.
In the original PageRank formula, link weight is divided equally among the number of links on a page. This undoubtedly does not hold true today, but it is still valuable in understanding the original intent.
Cross-linking makes the PageRank calculation much more complex. The key observation here is that when Page B links to Page A to make the link reciprocal, the PageRank of Page A (x) becomes dependent on f(y), the passable PageRank of Page B, which happens to be dependent on f(x)!. In addition, the PageRank that Page A passes to Page C is also impacted by the link from Page B to Page A. This makes for a very complicated situation where the calculation of the PageRank of each page on the Web must be determined by recursive analysis and search engine rankings.
We have defined new parameters to represent this: q, which is the PageRank that accrues to Page B from the link that it has from Page A (after all the iterative calculations are complete); and z, which is the PageRank that accrues to Page A from the link that it has from Page B (again, after all iterations are complete). More detail here in a better explanation about PageRank Sculpting
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 search engine rankings flows so that the five links without nofollow would flow one point of PageRank each.
It’s valuable to recall the illustration I put up on Google’s initial announcement of this change:
This change in Google’s treatment of nofollow links comes with some very interesting additional advice/clarification:
Q: Okay, but doesn’t this encourage me to link out less? Should I turn off comments on my blog?
A: I wouldn’t recommend closing comments in an attempt to “hoard” your PageRank. 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.
Many in the SEO field have long suspected that linking out to good places can provide a positive benefit, but I’m afraid that’s going to be very hard to quantify and therefore difficult to justify. In all honesty, I believe we’re going to see SEOs and websites revert to what I’ll call “old-school” PageRank sculpting – the kind prevalent prior to the existence of nofollow.
From now on, if you wish to sculpt PageRank, you’ll want to use one of the following classic PR sculpting methodologies:
- Option A: An embedded iFrame on the page containing the links you don’t want the engines to follow (remember not to link to the iFrame URL, and potentially block it using robots.txt)
- Option C: An embed in Flash, Java or some other non-parseable plug-in that contains the desired links
- Option D: Settings that turn off links for non-cookied or non-logged-in visitors
Tragically, while this action won’t hurt spammers or those seeking to manipulate Google, it will seriously harm many thousands of sites that have employed nofollow internally as it was long considered a best practice (and messaged as such to the SEO community by the same source as this reversal). I suspect it will be several years and many re-designs before a lot of sites are able to clean up this solution-turned-problem.
This is a disappointing move from Google on many fronts:
- It allows malicious operators to actively hurt a site by adding nofollowed links in comments, forums and other open submission arenas.
- It removes the protection webmasters thought was afforded by nofollowing links (you may not get hurt for linking to spam or paid links directly, but you’re now indirectly hurting your site’s PageRank flow)
- It casts doubt on Google’s credibility with future messaging to webmasters (Danny Sullivan covered this when he wrote about the loss of backwards compatibility
While I’m personally frustrated, I’m also thankful to Google for publicly messaging this in an honest, open way. I hope that in the future, we’ll get this notification in a more timely fashion. SEO consultants and in-house analysts are going to have their work cut out for them over the next few months.
p.s. Danny Sullivan’s comment on Matt’s blog post is also an essential read (and re-iterates many of the points above). A few valuable excerpts:
With this change, I can still get the $4 if I simply don’t allow comments. Or I show comments, but I use an iframe, so that the comment actually reside on a different page. In either case, I’m encouraged to reduce the number of links rather than let them be on the page period, nofollow regardless. If I’m worried my page won’t seem “natural” enough to Google without them, maybe I allow 5 comments through and lock them down after that.
Rather than clarify things, I feel like this is what your post is going to do — cause people to consciously reduce the number of links they allow on their pages. We’re going to see an increase in iframe usage or other techniques to reduce links and flow more PageRank to the remaining links, for those who really worry/believe in such things.
It’s been a long time since we had such a fundamental shift in SEO best practices (maybe the canonical URL tag, though it’s effectiveness has been questioned and this PR sculpting reversal isn’t likely to inspire confidence).