welcome Kevin
after a quick google ...careful with this kind of data. I skimmed through the paper really quickly.
my interpretation is there is not much out there in the way of good data.
things to watch for there appears to be a correlation between education and IQ. No doubt having a good education will no doubt help with IQ scores (and possibly the reverse?). So when looking religion and IQ it could really be education we are looking at. Or some other variable not measured. Just because there is correlation it does not mean there is a direct cause and effect. eg after the second world war there was a very good correlation between the increase in population in Belgium and the inrease in number of storks nesting on roofs.
attachment