According to researchers, Christians – particularly fundamentalists who believe the Bible is God’s word – have a lower IQ than those who are less religious.

A possible reason behind the finding was a tendency for more intelligent people to challenge religious claims, said one of the researchers, New Zealand psychologist Professor Tim Bates.

“If you believe in religion, you haven’t really questioned things,” he said. “Brighter people were less likely to feel that religion plays a dominant role in their life.”

To reach the conclusion, researchers from the University of Edinburgh compared the results of responses from 2300 adults with varying levels of religious belief. They rated themselves on a scale of one to five in response to a range of statements about their spirituality, religious identification, practices, support, mindfulness and fundamentalism.

Statements and questions included: “The Bible is the actual word of God”; “I feel God is punishing me for my sins or lack of spirituality”; and “How often do you pray in private?”

To measure intelligence, researchers carried out tests on recall, memory, verbal fluency, processing and reasoning. For example, participants were asked to recall a series of digits backwards and recite a list of words after a delay.

The researchers found higher IQ scores were significantly associated with lower scores on five of the six measures of religiosity – all except spirituality.

The strongest result was in the area of fundamental beliefs.

Intelligence was an “inoculation against fundamentalism”, with each 15-point increase in IQ making people about half as likely to have strong fundamentalist views, said Bates.

“People who claim The Bible is the literal word of God are typically less likely to be intelligent,” said fellow researcher Gary Lewis.

He and Bates agreed that those with higher IQs were more likely to challenge the claims made by religion.

The finding was a “fairly bold statement” to make, said University of Auckland Professor of theology, Elaine Wainwright.

She agreed fundamentalists were less likely to challenge religious beliefs, but questioned whether this was related to intelligence.

Intelligent people helped to progress religion in new directions, she said.