The whole question was raised by a series of correlation studies by Searchmetrics, Moz, and others that found "amazing" correlations between Google +1's and higher search rankings. These studies prompted Google's Distinguished Engineer Matt Cutts to find the politest way to debunk the idea that more Google +1's lead to higher Google rankings. This, in turn, prompted a serious discussion about the difference between correlation, causation, and coincidence. And this is what prompted Stone Temple Consulting to conduct a study of the impact of Google+ shares on search rankings. This is not a correlation study, but an actual measurement of causation. And the most surprising finding was: "Google Plus Shares did not drive any material rankings changes that we could detect." Get the full story at Search Engine Watch and Search Engine Land