Within the US, among 22 ranking factors identified, social signals account for 5 of the 6 most highly correlated with Google search results, according to a June 2012 study from Searchmetrics. Presenting the correlations using Spearman’s rank correlation coefficient, the study shows that Facebook shares (0.37) have the highest correlation, followed by number of backlinks (0.36). Other high-ranking factors include Facebook comments (0.33) and likes (0.3), and Tweets (0.25).
A number of factors display a negative correlation with Google rankings, including title character length (-0.04) and the position of title keywords (-0.05).
According to a BrightEdge survey released in January 2012, 84% of search marketers say social signals such as likes, tweets, and Google +1s will be either more important (53%) or much more important (31%) to their SEO this year as compared to 2011. Read the rest at MarketingCharts.