A study, done in 1998, consisting mainly of a survey of scientists in various fields to determine their religious belief.

Here are the results:

belief in a deity: 7%
agnostics and doubters: 20.8%
Nonbelievers: 72.2%

The study found the lowest levels of belief among biologists, with physicists and astronomers close. Mathematicians had the highest levels of belief at about 15%.