National Belief in God and Intelligence
All the studies on my "Religion and Intelligence" by Vexen Crabtree (2007) had concentrated on individual measurements of IQ, and how they correlate with religiosity. In the West, this largely correlates with Christian religiosity. Because most of these studies are performed in the West, it is possible that secularism and atheism is correlated with higher intelligence simply because Christianity has a particularly negative effect on intelligence.

To explore that further, I wanted to see if these trends exist in various cultures, where the background religion is no Christianity. Luckily for me, such studies have already been done, and have shown that across the globe, the more religious the people are, the less their average intelligence. It seems that the effects of belief on the Human search for truth are universal, and not religion-specific.

A study of data for belief in God and intelligence across 137 countries was undertaken by Lynn, Harvey & Nyborg (2009)9, with the latest comprehensive sets of data available, which were mostly from 2004. The data shows conclusively that countries with a higher average IQ have less belief in God - they state that "in only 17% of the countries (23 out of 137) does the proportion of the population who disbelieve in God rise above 20%. These are virtually all the higher IQ countries". Sociologists have found that in general, as a country gets more intelligence, the rate of belief in God begins to drop.

I've updated "Religion and Intelligence" by Vexen Crabtree (2007) and done a nifty graph showing this correlation in action.