A study The relation between intelligence and religiosity: a meta-analysis and some proposed explanations indicates that there is a relationship, with an abstract:
A meta-analysis of 63 studies showed a significant negative association between intelligence and religiosity. The association was stronger for college students and the general population than for participants younger than college age; it was also stronger for religious beliefs than religious behavior. For college students and the general population, means of weighted and unweighted correlations between intelligence and the strength of religious beliefs ranged from -.20 to -.25 (mean r = -.24).
Though it appears the access to the article is restricted, I would nevertheless like to understand better the claims made, and the scope of this and related studies.
In particular, I would like to know how sound the methods of the study are e.g. did they cherry-pick the 63 studies, or were these the only 63? Are there conflicting studies that have been left out?
As well, what do the authors mean by "religious" e.g. is the scope of the studies limited to only Christians in the USA?
All to express: How convincing is the methodology of this study, or any related studies proposing to answer this question?