Religious people are more likely to be less intelligent than atheists, according to a new study.

The study conducted by a team at the University of Rochester reviewed 63 other studies over the past decade that described the relationship between intelligence and religiosity. The results found that 53 out of the 63 studies found a negative correlation between smarts and believing in God, Yahoo reports.

"Most extant explanations (of a negative relation) share one central theme —the premise that religious beliefs are irrational, not anchored in science, not testable and, therefore, unappealing to intelligent people who 'know better',” the study concludes.

But the reasons for not believing may be more complex than the widely held conception that smart people “know better.” The study points to the fact that intelligent people are more likely to be married and successful in life, which may mean they need religion less in their lives.

One of the studies cited in the paper was one that followed a group of 1,500 highly intelligent children with IQs over 135. The study began in 1921 and continues until today. Once the children reached 75 to 91 years old, the children were considered less religious than the general population.

“Intelligent people typically spend more time in school—a form of self-regulation that may yield long-term benefits,” according to the study. “More intelligent people get higher-level jobs (and better employment (and higher salary) may lead to higher self-esteem and encourage personal control beliefs.”

Religiosity, researchers conclude, may boil down to function.

“People possessing the functions that religion provides are likely to adopt atheism, people lacking these very functions (e.g., the poor, the helpless) are likely to adopt theism,” the researchers wrote.

Researchers defined intelligence as the “ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience.” Religion was defined by involvement in some (or all) facets of religion.

Some argue the definition of intelligence is too narrow and does not include creative or emotional intelligence. The study’s subjects are also not representative of the world population – 87 percent of the paper’s participants came from the U.S., U.K. and Canada.

According to a recent study conducted by the University of California Berkeley, religious affiliations in the United States hit its lowest point since the 1930s – where 20 percent showed no religious preference.

"This was not happening really for decades, until around 1990, when it started to take off," Claude Fischer, one of the researchers with UC Berkeley, told The Huffington Post. "One thing striking is the trend in terms of renouncing religious affiliation you might say continues to move up at a regular pace, while there is hardly any perceptible trend in the percentage of people who express atheist or agnostic beliefs."