What is Page Authority?
Page Authority is a score (on a 100-point scale) developed by Moz that predicts how well a specific page will rank on search engines. It is based off data from the Mozscape web index and includes link counts, MozRank, MozTrust, and dozens of other factors. It uses a machine learning model to predictively find an algorithm that best correlates with rankings across the thousands of search results that we predict against.
How is Page Authority Scored?
We score Page Authority on a 100-point, logarithmic scale. Thus, it's easier to grow your score from 20 to 30 than it would be to grow from 70 to 80. We constantly update the algorithm used to calculate Page Authority, so you may see your score fluctuate from time to time.
What is Domain Authority?
Domain Authority is a score (on a 100-point scale) developed by Moz that predicts how well a website will rank on search engines. 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,
To determine Domain Authority, we employ machine learning against Google's algorithm to best model how search engine results are generated. Over 40 signals are included in this calculation. This means your website's Domain Authority score will often fluctuate. 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?
Domain Authority is scored on a 100-point, logarithmic scale. Thus, it's easier to grow your score from 20 to 30 than it would be to grow from 70 to 80.
What is MozRank
How is MozRank scored?
We calculate this score on a logarithmic scale between 0 and 10. Thus, it's much easier to improve from a MozRank of 3 to 4 than it is to improve from 8 to 9. An "average" MozRank of what most people think of as a normal page on the Internet is around 3.
Credits to http://www.seomoz.com