Google Webmaster Central Blog: “Developing algorithmic changes to search involves a process of experimentation. Part of that experimentation is having evaluators—people who assess the quality of Google’s search results—give us feedback on our experiments. Ratings from evaluators do not determine individual site rankings, but are used help us understand our experiments. The evaluators base their ratings on guidelines we give them; the guidelines reflect what Google thinks search users want. In 2013, we published our human rating guidelines to provide transparency on how Google works and to help webmasters understand what Google looks for in web pages. Since that time, a lot has changed: notably, more people have smartphones than ever before and more searches are done on mobile devices today than on computers. We often make changes to the guidelines as our understanding of what users wants evolves, but we haven’t shared an update publicly since then. However, we recently completed a major revision of our rater guidelines to adapt to this mobile world, recognizing that people use search differently when they carry internet-connected devices with them all the time. You can find that update here.”