The big Google updates of recent times have led to a rethink by many SEOs: It's no no longer just about individual and clearly identifiable factors. Increasingly its the user behaviour in response to the user experience that determines the success of Google. What it is, whether it's a ranking factor and, importantly, what Google says, is covered in this blog post.
https://www.sistrix.com/blog/is-user-experience-a-ranking-factor/
