Since most of the studies Frako mentioned earlier are pretty old, I thought I mention a
newer one. From the abstract:
quote:
Evidence is reviewed pointing to a negative relationship between intelligence and religious belief in the United States and Europe. It is shown that intelligence measured as psychometric g is negatively related to religious belief. We also examine whether this negative relationship between intelligence and religious belief is present between nations. We find that in a sample of 137 countries the correlation between national IQ and disbelief in God is 0.60.
I also remember reading a study in a Dutch newspaper that they found that IQ in immigrants from Muslim countries and their children was structurally underestimated in tests due to cultural differences. These tests take, for example, knowledge of Snow White and what she stands for for granted, but this knowledge is less common in (non-Western) immigrant communities. Given that these communities tend to be (on average!) more religious, such a cultural difference might be easily misinterpreted as a religious difference.