Religion and intelligence
Edward Dutton has kindly just sent me a PDF of his 2014 book under the title above. It is a very comprehensive and research-based treatment of its topic. And I will mention his most striking finding straight away: Churchgoers are just as intelligent as atheists.
The big problem with research in the area is defining religion. There are all sorts of religions. A major religion these days is "Belief in God only". Does that count for anything? And what about Leftism? It has many of the characteristics of a religon. Should it be included? So we cannot be too surprised to note that the various research studies show no uniform definition of religion.
And even people of the same religion may have very different beliefs. A Catholic who attends mass regularly will usually have much different beliefs than one who has not been to mass for years. So direction of belief and strength of belief need to be sorted out too.
I can think of some solutions to those problems but none of the studies so far have addressed them adequately, as far as I can see. But, out of what's available, the best indicator of religious belief would seem to be church attendance, or "religious practice" more broadly. It too does of course have its weaknesses. It is very well known that some people attend church for social rather than religious reasons. They may even go just for the coffee and cake afterwards. But there can surely be very few church attenders who are totally non-religious. And when we think of religious people, it is surely churchgoers whom we are most likely to have in mind.
Table 7.2 on p. 180ff of Dutton's book gives the correlations between churchgoing and IQ. Most are very low indeed and all but one are less than .20. And a correlation of .20 reflects only 4% common variance between the two factors, so is negligible.
As it happens, the correlation with religious belief that Dutton tabulates are also low, though not as low as the correlations with religious practice. The majority are in fact less than .20.
So the conclusion has to be that IQ is unimportant as an explanation of religious belief.
And if someone wants to get Marxist with me and say that I draw that conclusion only because I am myself religious, I reiterate what I have often said before: I am the most utter and complete atheist