Can it possibly be true that the Tinder and hookup generation is actually unusually chaste?

A new study says it can, and one of the authors, a professor in the Center for Human Sexuality Studies at Widener University, is convinced it is - with some caveats.

The study, based on surveys conducted between 1972 and 2014, found that the number of 20- to 24-year-olds who said they had not had any sexual partners since age 18 was more than twice as high for millennials born in the 1990s as for Generation Xers born in the late 1960s: 15 percent vs. 6 percent.

The trend was restricted to whites, and was more pronounced in women than men.

College attendance either was or was not an important factor, depending on how the numbers were analyzed.

The study, which examined 26,707 responses to the national General Social Survey, was conducted by Jean Twenge at San Diego State University, Ryne Sherman at Florida Atlantic University, and Brooke Wells at Widener. It was published Tuesday in the Archives of Sexual Behavior.

Last month, the same team, using results from the same survey, published a study that found that growing numbers of Americans were having gay sex and that attitudes toward same-sex behavior had grown more positive.

The survey asks people only what they're doing, not why, so the researchers can only guess at explanations for sexual inactivity. One possibility: The survey asked about sex, but people define the word differently. Another: More twentysomethings are living with their parents.

"Certainly, living with your parents makes having sex a little more complicated," Wells said.

A different survey from the U.S. Centers for Disease Control and Prevention found that the percentage of high school students who said they were virgins increased from 46 in 1991 to 59 in 2015.

Overall, studies have also shown that recent "emerging adults" - those 18 to 29 - have been slower than previous generations to embrace adult responsibility. That includes marriage, a traditional way to have access to a steady sex partner. The percentage of 18- to 32-year-olds who were married fell from 48 percent of baby boomers (born 1946 to 1964) to 36 percent of Gen Xers (born 1965 to 1979) to 26 percent of millennials (born 1980 to 1994).

Meanwhile, Americans have generally become more accepting of premarital sex, but individualistic millennials "may feel less pressure to conform in their own behavior," the authors wrote.

Lulu Steurer, 20, a Syracuse University landscape architecture major whose family is in Haddonfield, sees some of her friends putting off marriage. But, she said, "they're not waiting until marriage to have sex."

The results of the study surprised her. She said she knows more women who are having sex than aren't. "I would think that today, women would be having more sex - Tinder, social media . . . it's easier to find people. And it's socially acceptable" for women to have sex.

Patrick Munn, who will be studying biology at the University of Pennsylvania this fall, said he knows two men, both 20, who are waiting for marriage to have sex. But Munn, 18, said they are the exceptions in his peer group, perhaps because "people are less religious."

"In my experience, no one is really waiting," agreed Ren Chock, 19, a New College of Florida student who is working in Philadelphia for the summer. "With Tinder and other sites, if someone wants to find sex, they will."

Jordan Chamberlain, 24, an English major at West Chester University, was surprised that the survey showed a difference between men and women when it comes to sexual activity. "I know a lot of girls who are comfortable with their sexuality," she said. "But what they're vocal about may be different than what they're doing."

Wells thinks definitions could be a problem. The survey doesn't define what sex means. Some young people don't think of oral sex or even anal sex as sex. This could stem in part, she said, from abstinence-only sex-ed classes or chastity pledges that focused on sexual intercourse.

College hookups, she said, often do not include vaginal sex.

Steurer said that she considers both intercourse and oral sex to be sex and thinks her friends would agree.

Lindsey Nice, a 24-year-old tech start-up project manager who lives in the Graduate Hospital area, said she and her friends consider a lot of things sex: "In the LGBT community, there's a wider definition of sex."

One might think that the popularity of apps like Tinder, which lets users swipe left to reject or right to accept potential matches, would increase sexual activity. But, the study said, its focus on pictures may leave less attractive young people out in the cold.

Plus, Wells said, "you can spend all night on Tinder swiping faces and never hook up with anybody."

Nice said that for the LGBT community, "social media has helped us find sex."

Social media also increase the size of the dating pool. "The options are out there," Chamberlain said, "but women are more particular."

Steurer agreed. "With social media, there are so many options, you can't make a decision," she said. "You're waiting for the next person to come along." And because people present the best version of themselves online, "you're nervous to meet them. You [might] not [be] meeting the standard you set for yourself."

Other possibilities for the study's findings are that young people, who face a tough job market, are putting more of their energy into their careers. They also have more opportunities for entertainment than older generations.

Wells said researchers need to explore how to define sex to understand generational behavior better. She said young people also seem more accepting of consensual nonmonogamous relationships, another area that will require precise questioning.

Another unresolved issue is what role education plays. Based on the survey alone, the percentage of sexually "inactive" 20- to 24-year-olds rose from 6 percent to 10 percent among those who hadn't gone to college and from 6 percent to 19 percent among those who had at least some college. But a more complex analysis that included all age groups found the trend was stronger in people who had not attended college.

As for the 85 percent of young millennials who are having sex, Wells said there is evidence they're having more casual sex than previous generations, although some of that may be of the steady, friends-with-benefits variety.