Atheists tend to be highly educated1. 27% of the general population have college degrees, while 43% of atheists claim the same. The more educated a person is, the more capable he or she is at critical thinking2. This of course does not guarantee that education will turn a person into an atheist, possibly due to the fact that many people find comfort in their religiosity. And then there is the factor of some religious individuals adhering to the beliefs that still make sense in the modern world, but forgoing those that no longer make sense2.
Gallup found in 2010 that the lower a country’s per capita income, the higher their population rates the importance of religion3.
Is religion an important part of your daily life? (Median responses among countries at each per-capita income level.)
Note that the US breaks the statistics with a higher than average percentage of religiosity (65%) compared to wealth (about $49,000).