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Why Domain Authority Is A Better SEO Metric Than PageRank

October 12, 2012

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pagerankMany SEOs place far too much weight on Pagerank as an SEO metric.  While a strong Pagerank is certainly correlated with higher rankings and serves well as an official measure of raw “link juice”, the Pagerank score barely begins to scratch the surface of what we can learn about a site or page by digging a little deeper.

This isn’t to say that Pagerank isn’t important – it’s certainly important to be aware of Pagerank while going about your daily SEO tasks.  However, Pagerank often receives too much focus as an SEO metric, when it’s only a single, small factor in the way Google analyzes the value of links.

What Is Domain Authority?

Domain authority (and page authority) is an SEO metric measured on a logarithmic scale from 0-100 produced by SEOmoz.  It’s not actually used by Google to rank sites, but rather SEOmoz uses machine learning algorithms to model Google’s ranking factors and determine the signals that are incorporated into domain authority.  The domain authority metric incorporates over 150 linking signals, raw “link juice” being just one of the factors.

Why Is Domain Authority A More Useful SEO Metric Than Pagerank?

In essence, domain authority is a much better representation of the many linking signals Google uses in calculating the search engine ranking pages (SERPs).  Pagerank on the other hand, only calculates one small aspect of the linking equation.  In other words, Pagerank is a measure of the raw “link juice” of a page – which is an important ranking factor – but we know that the modern version of the Google algorithm looks at many other factors beyond raw link juice when analyzing links.

As Google’s head of web spam Matt Cutt’s has stated, Pagerank is just one of several hundred algorithm ranking factors, and only one of the many link metrics Google analyzes.  Domain authority/page authority on the other hand, attempts to model the many other link metrics Google uses in analyzing links, with Pagerank being just a single factor in calculating domain authority.

Domain Authority Incorporates Trust

One important ranking factor that gets incorporated into SEOmoz’s domain authority metric is trust.  While no one knows exactly how Google determines a site’s trust, we do know that Google has a patent filed for TrustRank, which is based on the link distance from a trusted seed source.  We know this is an important ranking factor that doesn’t get taken into account through Pagerank .  Trust is certainly correlated with Pagerank, since trusted sites tend to have more links, but the inverse is not necessarily true, since plenty of shady or spammy sites have a massive volume of links.

Domain authority/page authority, like Trustrank, measures a site or page’s trust by taking into account a site’s link distance from a trusted seed source (think sites like Wikipedia.org, Amazon, Nasa.gov, Harvard.edu, Cnn.com etc).  A site that’s linked to directly from Whitehouse.gov and Stanford.edu is probably trustworthy, and any site it links to may benefit from that trust as well.  On the other hand, a site with 1,000,000 links but none of them from a trusted seed source is probably not trustworthy, despite having plenty of link juice and a high Pagerank.

Domain Authority Incorporates Number Of Unique Linking Domains

This is another area where using Pagerank as a metric can be deceiving.  While a site’s internal page can gain Pagerank even with no outside links, the number of unique domains linking to a page is another important ranking signal.  While this metric is incorporated into the domain/page authority calculation, it’s completely neglected if one only looks at Pagerank.

Pagerank is not very specific

Beyond the additional factors that get taken into account with the domain authority metric, Pagerank’s logarithmic scale of 0-10 is not very specific, making it hard to use precisely as an SEO metric. Because the logarithmic scale of each Pagerank level is based on a factor of somewhere between 8-10 (no one knows for sure, but these are best estimates), a low Pagerank 5 page may actually have 8-10 times less “link juice” than a high Pagerank 5 page.  The more precise 1-100 logarithmic scale offered by domain authority/page authority metrics is much more useful for practical purposes.

Pagerank is updated infrequently

While Google continually recalculates Pagerank as its bots crawl the internet, the “toolbar” Pagerank numbers available to the public are updated extremely infrequently, perhaps only once every 2-3 months.  Because the linking environment on the internet is in a constant flux, this outdated data makes it more useful as a broad indicator rather than a precise SEO metric.

Look Beyond Pagerank In Your SEO Efforts

While Pagerank certainly has its place in an SEO’s toolbox – if you’re analyzing competition, looking for linking opportunities, looking for sites to purchase, or analyzing your own SEO efforts – domain authority may be a more useful metric.

About the Author:

Nate Ryerson is a full-time SEO and part-time blogger for Whoishostingthis.com – an Alexa Top 10k web property. You can get more information about their hosting reviews at their company site.

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