Domain Authority? Domain Authority represents SEOmoz's best prediction about how a website will perform in search engine rankings. Use Domain Authority when comparing one site to another or tracking the “strength” of your website over time. We calculate this metric by combining all of our other link metrics (linking root domains, number of total links, mozRank, mozTrust, etc.) into a one single score.
To determine Domain Authority, we employ machine learning against Google's algorithm to best model how search engine results are generated. Over 150 signals are included in this calculation. We constantly refine this model over time. This means your website's Domain Authority score will often fluxuate. For this reason, it's best to use Domain Authority as a competitive metric against other sites as opposed to a historic measure of your internal SEO efforts.
How is Domain Authority Scored?
We score Domain Authority on a logarithmic scale ranging from 0 to 100-points. Thus, it's far more challenging to grow your score from 70 to 80 than it would be to grow from 20 to 30.
Domain Authority vs. Page Authority
Whereas Domain Authority measures the predictive ranking strength of entire domains or subdomains, Page Authority measures the strength of individual page. The same is true for metrics such as MozRank and MozTrust.
Where can you find Domain Authority?
Domain Authority metrics are incorporated into dozens of SEO and online marketing platforms across the web.
You can measure Domain Authority using Open Site Explorer or the MozBar,
Technical Definition of Domain Authority
Domain Authority is SEOmoz's calculated metric for how well a given domain is likely to rank in Google.com search results. It is based off of the Linkscape web index and includes link counts, mozRank, mozTrust, and dozens more. It uses a machine learning model to predicatively find an algorithm that best correlates with rankings across thousands of search results that we predict against.
It's best to use Page Authority (PA) and Domain Authority (DA) as comparative metrics when doing research in the search results and determining which sites/pages may have more powerful/important link profiles than another. While more specific metrics like mozRank can answer questions of raw link popularity and link counts can show the raw quantities of pages/sites linking, the authority numbers are high level metrics that attempt to answer the question "How strong are this page's/site's links in terms of helping them rank for queries in Google.com?"
SEO Best Practice
How do I influence this metric?
Unlike other SEO metrics, Domain Authority is difficult to directly influence. This is because it is made up of an aggregate of metrics (mozRank, mozTrust, link profile, etc...) that each have an impact on this score. This was done intentionally because this metric is meant to approximate how competitive a given site is in Google.com. Since, Google.com takes into account a lot of factors, a metric that tries to calculate it must incorporate a lot of factors as well.
This means the best way to influence this metric is to improve your overall SEO. Particularly you should focus on your link profile (which influences mozRank and mozTrust) by getting more links from other well linked to pages.