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.
Backlinks continue to be one of the most critical factors affecting rankings, according to the Searchmetrics report. The number of backlinks ranks just behind Facebook shares as the most highly-correlated factor. Additionally, other backlink factors also positively correlate, such as the proportion of nofollow links (0.15) and the proportion of links containing keywords (0.10).
Further results from the report indicate that too much advertising can be a dampener on search ranking success. The advertising factors studied all returned a negative correlation: AdLinks; AdSense; and AdSense Blocks each had a correlation coefficient of -0.04. Even so, the report notes that the correlation value for Adlinks includes AdSense, and separating out AdSense, which has a negative correlation, yields a better result for Adlinks.
Also, Searchmetrics indicates that this result needs to be monitored, as these factors only appear to be relevant in the top 10 results and because AdSense tends to feature more often on poorly ranking sites than those with better rankings.
About the Data: The report cautions that correlation does not equate to causation, and these results do not in any way guarantee that the factors have an effect on rankings or are even used by Google as signals.
For its dataset, Searchmetrics selected an extremely large keyword set of 10,000 search terms from Google.com U.S. Searchmetrics did not just include the top 10,000 search terms according to search volume, since they contain a disproportionately high number of brand keywords which might have distorted the assessment of many other key factors. Instead the reference dataset includes a mix of different keywords with, if not the largest, then at least generally high search volumes. Around 1 in 10 are keywords that were identified as navigation-oriented according to Searchmetrics logic; the rest are a mix of keywords from a variety of CPC areas to best cover transactional (higher CPC) and information oriented (lower CPC) searches as well as the hybrids in between.
The assessment was limited to organic searches – AdWords, Universal Search OneBoxes, 2 to 7 packs, sitelinks, iGoogle integrations etc. were not included. The analysis’ 10,000 analyzed keywords lead to: 30,000 SERPs with 300,000 titles, descriptions and URLs. The ranking sites’ content included: 14.68 GB in data; 92,672 AdSense blocks; 338,562,612 Facebook comments; 3.04 billion shares; and 8.1 billion likes.
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