The Panda process

Google Panda was built through an algorithm update that used artificial intelligence in a more sophisticated and scalable way than previously possible. Human quality testers rated thousands of websites based on measures of quality, including design, trustworthiness, speed and whether or not they would return to the website. Google's new Panda machine-learning algorithm was then used to look for similarities between websites people found to be high quality and low quality.
Many new ranking factors have been introduced to the Google algorithm as a result, while older ranking factors like PageRank have been downgraded in importance. Google Panda is updated from time to time and the algorithm is run by Google on a regular basis. On April 24, 2012 the Google Penguin update was released, which affected a further 3.1% of all English language search queries, highlighting the ongoing volatility of search rankings.
On September 18, 2012, a Panda update was confirmed by the company in its official Twitter page, where it announced, “Panda refresh is rolling out—expect some flux over the next few days. Fewer than 0.7% of queries noticeably affected"^[7]
Another Panda update began rolling out on January 22, 2013, affecting about 1.2% of English queries.^[8]