In 1921, a study began out of the University of Rochester to determine whether there was any correlation between intelligence and religious beliefs. The study followed 1,500 “gifted” children—those with IQs over 135—over the course of their lives, monitoring their continued spiritual and intellectual development.

The study continues to this day, and the team behind the study has found “a reliable negative connotation between intelligence and religiosity.” In other words: Atheists tend to be more intelligent than religious people.

Initially, it was assumed intelligent people shy away from religion because they’re uncomfortable with abstracts like faith and spirituality, preferring scientifically provable subjects. However, more recent research suggests the real reasons are a bit more involved.

The researchers claimed religion’s psychological benefits, such as self-fulfillment, don’t hold as much appeal to atheists, because they feel capable of providing those things for themselves. Basically, atheists feel capable of getting religion’s perks on their own. Religious people, on the other hand, are on the hunt for something outside of themselves to give their life meaning and purpose.

If that’s the case, it makes some less-known research out of the University of Illinois all the more interesting. It’s a Twitter-based study, so it requires a grain of salt, but it’s still fascinating. It followed two groups of people: ones who followed prominent Christians on Twitter, and ones who followed prominent atheists. The study found the first group—presumably the more “Christian” group—was far more likely to be positive and optimistic. The second group was more likely to use words that convey negative emotions.

The Twitter study is much less comprehensive, but it does beg the question: If atheists are truly shunning religion because they feel more capable of achieving satisfaction and purpose on their own, what does it mean that their outlook is more negative?