SEO experts often perform massive studies of the Web, trying to figure out what the best way to rank on Google actually is.  Dozens of theories have been proposed, and they change as Google changes its algorithm.  A decade ago, it was PageRank that seemed to be all-important; a short time after that it was the total authority of your incoming link funnel.  But through all of it, there has been one attribute that has been the most consistent in matching up well with your Google rank: the number of unique root domains that your page has incoming links from.
linking root domains
The Power of Unique Root Domain Backlinks
For example, let’s look at a hypothetical webpage.  This webpage is new, and it’s focused on a keyword with remarkably low competition – only 400 competing pages.  The website’s author has a friend that works for Wikipedia, and manages to get the page linked to from seven different pages on Wikipedia.  That’s a lot of authority, and the page gets quickly indexed and appears in the #1 spot for it’s keyword on day one.

Then, along comes another webmaster who has stumbled upon the same phrase, and wants to win.  He doesn’t have a friend at Wikipedia, but he does know the value of unique root domains.  He starts a blog on WordPress, writes a Squidoo lens, gets his site listed in the Yahoo! Web Directory, puts an article up on EzineArticles.com, fits his website into an answer at Wis.Dm and squeezes in a guest post on a friend’s blog that has it’s own unique URL.  That’s six different unique root domains — none of which has the authority and power of Wikipedia behind it — but the effect is that he knocks the first webpage off of the #1 spot less than a week after he went into business.

Some Important Details
Just to be clear, what we’re talking about is the number of unique root domains linking to your website versus the number of unique root domains linking to your competitors’ websites for any given keyword.  For example, if the keyword is “betta fish” and you have 120 unique root domains linking back to you and your competitor has 150, chances are good that he will outrank you. For the keyword “fighting bettas”, however if the number one spot has only 90 unique root domains linking to him, your 120 are likely to defeat him and take the number one spot.

It should be noted that while the number of unique root domains linking to your website is a strong indicator of your website’s potential rank for any given keyword, it is only a strong indicator.  The best studies indicate that the statistic is wrong in just over a quarter of all cases — so there are clearly a lot of other factors to take into account.

How to Take Advantage
The outcome of this research is clear: if you want to rank highly for any given keyword, your first goal should be to record the number of unique root domains linking back to the top 3 sites for that keyword, and do whatever it takes to obtain backlinks from more unique root domains than they have.  It might not win the day on it’s own, but it’s a very solid place to start.