Of the sixteen studies thirteen of them, 81%, showed an inverse correlation between religiosity and intelligence. That is, the aggregate scores were consistently highest among the least religious / non-believers, and lowest among the more religious / most religious. While three studies reported no statistical difference between the groups, not a single one of the studies reported higher intelligence in the religious groups Vs the less religious / non-believer groups.
A list of those studies follows for those who would like to research this further:
Thomas Howells, 1927
Hilding Carlsojn, 1933
Abraham Franzblau, 1934
Thomas Symington, 1935
Vernon Jones, 1938
A. R. Gilliland, 1940 (no statistical difference)
Donald Gragg, 1942
Brown and Love, 1951
Michael Argyle, 1958
Jeffrey Hadden, 1963 (no statistical difference)
Young, Dustin and Holtzman, 1966
James Trent, 1967 (no statistical difference)
C. Plant and E. Minium, 1967
Robert Wuthnow, 1978
Norman Poythress, 1975
Wiebe and Fleck, 1980
Another example, the Brown and Love (’51) study, tracked controlled test scores. Believers’ averaged 19% lower average test scores than did non-believers.
I have discussed in earlier posts the fact that the most eminent scientists in the US and Great Britain, members of The National Academy of Science, and the Royal Society, have much lower rates of religious belief than does the general population of either country.
So when we take all this data into account, what conclusion can we draw? Well, we cannot infer that all atheists are smarter than all theists. That would be an easily falsified assumption. But we can deduce by a preponderance of corroborating results from scientifically conducted studies that on the aggregate atheists are more intelligent than believers.
The reason for this is not difficult to surmise. People who can best access problems using reason, fact and logic use those same attributes to analyze / examine the claims of theistic belief. When they do they conclude those claims to be lacking. People with lesser degrees of those attributes are least likely to apply critical thinking to religious claims, and are more inclined to accept them at face.
The evidence for this is overwhelming and not a recent observation. Celsus, a 2nd century Greek writer was a careful observer of the early Christian movement and critic of it. Among his many observations are the following:
"… the following are the rules laid down by them [ Christian proselytizers] . Let no one come to us who has been instructed, or who is wise or prudent (for such qualifications are deemed evil by us); but if there be any ignorant, or unintelligent, or uninstructed, or foolish persons, let them come with confidence. By which words, acknowledging that such individuals are worthy of their God, they manifestly show that they desire and are able to gain over only the silly, and the mean, and the stupid, with women and children."...
The least educated, least discerning, most ignorant and gullible are those least likely to challenge and question, and the more likely to blindly accept faith over fact. This is just as true of Islam, the fastest growing religion in the world thanks to its appeal to the most undereducated inhabitants of the Third World.