I think when you're talking about a study of studies, rather than a single study, and when the results are as comprehensive as those results, it seems most probable that there is a relationship.
When you consider that of the most eminent scientists in America, those elected into the National Academy of Sciences - only 7% believe in God and of American scientists not elected into the Academy - only 40% believe in God (compared with the astounding 90% national figure) and when you consider that of the equivalent organisation in the UK - the Royal Society - only 5% believe in God, I think it's clear that there is a relationship between intelligence and belief in God - at least the socially accepted definition of intelligence. Consider this, there have been 43 studies into the relationship. 39 have found that the higher the intelligence the lower the chance of believing in God. 4 have found no relationship. The vast majority of scientists in the top scientific fellowships of the US and the UK also do not believe in God. While this is not conclusive evidence, there seems to be only one conclusion that can be drawn from this.
"Religion is regarded by the common people as true, by the wise as false, and by the rulers as useful." Seneca the Younger 4 b.c.- 65 a.d.