"The core finding is that the association between graduating from college and religious disaffiliation has changed drastically across generations," said Philip Schwadel, the study's author and a professor at the University of Nebraska-Lincoln. For people who were born in the 1920s and '30s, the godless-college-grad stereotype is somewhat true: They were twice as likely as their uneducated peers to be religionless, not identifying with a particular church or synagogue or other religious institution.

But over time, that trend changed. "For those people who were born in the 1960s, there’s really no difference between the college-educated and the non-college-educated in terms of their likelihood of disaffiliating from religion," Schwadel said. "And for those born in the 1970s, it’s actually the non-college-educated who are relatively likely to disaffiliate."

This may have happened for a few reasons, Schwadel said. "The growth in college education may have led to a different population of people going to college." In the 1920s, only elites attended universities; especially at a time when religiosity was almost uniformly part of American life, it makes sense that this very small group of top intellectuals were the most likely to reject religion. Now that higher education has gotten somewhat more economically diverse and a lot more widespread, though, it seems natural that intellectual diversity at the university level has grown, too.

But that doesn't explain Schwadel's most surprising finding: For people born during the 1970s, not going to college makes you more likely to say that you're not religious.

The reason for this may be that atheism, agnosticism, and general religious indifference has become more normal across social classes, Schwadel said. "For those people who were born earlier than the 1900s, it might have been something that wasn’t acceptable among a lot of Americans, except those who were among the upper classes—those select few who were going to college and graduating in the 1910s, ‘20s, and ‘30s. But as college education has grown, having no religious affiliation has become less ostracizing."

As for the idea that college communities are inherently hostile to faith, Schwadel said the opposite is actually true. "Today’s campuses have many religious groups that students can participate in, along the lines of Greek and fraternity and sorority houses," he said.

There are a couple of important limitations to Schwadel's study. First, his study measures religious affiliation, not religiosity—it looks at how many people identify as Catholic, Jewish, etc., but it doesn't take into account how regularly they go to services. Studies have indicated that Americans often lie about how much they go to church, so measuring religious affiliation doesn't necessarily reveal a lot about how much people actually care about God.