n a 2013 meta-analysis, led by Professor Miron Zuckerman, of 63 scientific studies about IQ and religiosity, a negative relation between intelligence and religiosity was found in 53, and a positive relation in the remaining ten. Controlling for other factors, they can only confidently show strong negative correlation between intelligence and religiosity among American Protestants.[1][2]
The relationship between countries' belief in a god and average Intelligence Quotient, measured by Lynn, Harvey & Nyborg.[11]
Nyborg also co-authored a study with Richard Lynn, emeritus professor of psychology at the University of Ulster, which compared religious belief and average national IQs in 137 countries.[11] The study analysed the issue from several viewpoints. Firstly, using data from a U.S. study of 6,825 adolescents, the authors found that atheists scored 6 IQ points higher than non-atheists.
Secondly, the authors investigated the link between religiosity and intelligence on a country level. Among the sample of 137 countries, only 23 (17%) had more than 20% of atheists, which constituted “virtually all... higher IQ countries.” The authors reported a correlation of 0.60 between atheism rates and level of intelligence, which was determined to be “highly statistically significant”