The study released last week by PRRI, a polling group that specializes in studies of faith and values, adds to a research trend showing a dramatic increase in the number of Americans who declare themselves unaffiliated with any religion. In 1991, only 6% of survey respondents declared themselves “unaffiliated.” In the new study, that number has risen to 25%, making the unaffiliated “the single largest ‘religious group’ in America,” the study found.

The impact is most dramatic among young people. In 1996, 20% of Americans between the ages of 18 and 29 declared no religious affiliation. In 2016, that number has risen to 39%.

“This is a new generational dynamic,” PRRI CEO Robert Jones, and not just a function of young people rejecting their parents’ faith and then trending back to religion when they get older. “We have pretty good data that suggests that’s highly unlikely,” Jones said. The survey data indicates that people who were raised unaffiliated are half as likely to join a faith community in adulthood as their parents’ generation was. That means that people now under 30 will be for decades to come “the most religiously unaffiliated generation we have seen since we have been tracking modern statistics.”