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Domain Authority is a measure of how well a website is likely to perform in search engine results. It’s a search engine ranking score developed by Moz to give an overview of likely site performance. After Google deprecated and then stopped publishing PageRank, DA became one of the go-to replacements.
Notice, I said ‘likely.’ Google doesn’t rank by site, it ranks by pages. And as Danny Sullivan says at Search Engine Land: Google ‘has no single “authority” metric.’ Google uses a ‘bucket of signals,’ Sullivan says. Similarly, Moz uses its own collection of metrics to arrive at a site’s DA – over 40 of them.
These include MozRank, MozTrust and other Moz-proprietary factors. It’s a complex algorithm, though as SEOBlog’s Eric Sornoso notes, ‘not as complex as Google’s ranking itself.’ And it’s logarithmic. If you’ve never encountered a logarithmic scale before these graphics will help.