The 2012 LW Survey included a few questions that measured standard biases from the heuristics and biases literature. The general pattern was that LWers showed less bias on those questions than the university students in the published studies that the questions were taken from, and that people with closer ties to LW (read more of the sequences, higher karma, attend meetups, etc.) showed less bias than people with weaker ties.

This doesn't necessarily mean that reading the sequences (and getting involved in LW in other ways) causes the reduction in bias on those questions - it could just be that the people who have read the sequences will tend to show less bias on these questions for other reasons. In order to do more rigorous testing with randomization, we'll need smaller/quicker interventions than "read the sequences" (which is something that CFAR is working on).