Every now and again a new SEO rankings factor correlation study is published, showing which elements of SEO correlate best with high rankings in Google. Take for example this 2013 study from Searchmetrics, or the (now-retired) Open Algorithm research.
In and of itself these correlation studies are usually not a bad thing. If performed correctly these correlation studies can provide valuable data about SEO.
The problem usually arises when people start to create hypotheses about the causal relationships between rankings and the correlated factors. Recently this became very clear in Cyrus Shepard’s thorough and well-researched post that showed a strong correlation between Google+ and high rankings in Google.