American adults of every age group are having less sex than they were a generation ago , suggests a study published Tuesday in the Archives of Sexual Behavior.

Specifically, Americans born in the 1980s and 1990s are having less sex than those born in the 1960s and 1970s had at the same age despite their reputation for relying on dating apps to set up sexual encounters and preferring hookup culture to traditional courtship.

The study, which included data from 26,000 adults, compared sexual activity among Americans in the late 1990s to the early 2010s. It found that adults had sex an average nine fewer times per year in the early 2010s than in the early 2000s.

The decline in sex was even steeper for Americans who were married or living together. Co-habitating adults had sex an average 16 fewer times per year in the early 2010s than in the early 2000s.

We ended up identifying two major reasons for the decline, said study author Jean Twenge, a psychology professor at San Diego State University and author of the book Generation Me. Fewer people have steady partners [and] the people who do have steady partners are having sex less often.