In fact, although the United States is one of the most religious developed countries in the world, most Americans scored 50 percent or less on a quiz measuring knowledge of the Bible, world religions and what the Constitution says about religion in public life.
The survey is full of surprising findings.
For example, it's not evangelicals or Catholics who did best - it's atheists and agnostics.
It's not Bible-belt Southerners who scored highest - they came at the bottom.
Those who believe the Bible is the literal word of God did slightly worse than average, while those who say it is not the word of God scored slightly better.
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Smith has a theory about why atheists did so well on the quiz - they have thought more about religion than most people.
"Very few people say that they were raised as atheists and agnostics," he explains.
About three out of four were raised as Christians, he says.
"They were raised in a faith and have made a decision to identify themselves with groups that tend to be fairly unpopular," atheists and agnostics, he says.
"That decision presupposes having given some thought to these things," which is strongly linked with religious knowledge, he says.