Search engine optimization has not been dependent on a minimal number of factors for a long time now, such as number of times a keyword appeared on a page, and it continues to become a more complex web of on and off-page factors every month.
One of the more recent factors that has had an impact on search ranking is social media.
Wow! One fact on this Infographic says tweeting cuts time to index by half!
See on beingyourbrand.com