Americans Are Having Less Sex: By the Numbers
Adults in America are having less sex than in previous decades.
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Sexual activity across America has dropped in recent years.

In 2014, U.S. adults were having sex an average of 53 times per year, which is nine fewer times annually than the average between 1989 and 1994, according to a new study. And the researchers found that the sexual slowdown is happening across different ages, geographic regions, races, levels of education and genders.

The steepest sexual declines over time occurred among married people, people in their 50s, people with children ages 6 to 12, people with college degrees and people who hadn't seen a pornographic movie in the past year, the study authors found. [The 10 Most Surprising Sex Statistics]

The researchers looked at data from about 26,000 adults in the U.S. across all age groups, over a 25-year period, from 1989 to 2014.

The study ruled out lingering questions from prior studies about how the use of pornography or longer working hours might affect people's sexual activity: More work and more porn usually meant more sex, the authors found.

Instead, two factors emerged as the likeliest explanations for Americans' widespread sexual slump.

The number of people in the U.S. who are not in relationships has gone up. An estimated 64 percent of Americans ages 18 to 29 were not living with a partner in 2014, up from 48 percent in 2005. And people without regular partners generally have less sex than those with a steady squeeze, study co-author Ryne Sherman, an associate psychology professor at Florida Atlantic University, told Live Science.

"Unpartnered people have sex less frequently — about half as often as partnered [people] — across the time period we looked at and across all age groups," Sherman said.

So when the percentage of unpartnered individuals in the general population increases, it's not surprising to see a drop in the amount of overall hanky-panky going on, he said.

However, the study also revealed that people in relationships were also having less sex than that group had in the past. In 2014, people with regular partners had sex about 55 times, on average, down from an average of 73 times in 1990, the scientists discovered. [The Science of Breakups: 7 Facts About Splitsville]

"Partnered people always had an advantage in sex frequency over unpartnered people, and that advantage is narrowing," Sherman said. "That was something we didn't anticipate, and we don't have great answers for why that's the case."

Of all the generations represented in the study, millennials — people born between the 1980s and the early 2000s — were the least sexually active. In an earlier study, they were found to be having less sex than 20-somethings in previous generations, with about 15 percent of millennials ages 20 to 24 reporting that they had been abstinent since age 18.

Millennials may be less sexually active because many of them are living with their parents longer and taking more time to become financially independent, due to the economic downturn in the late 2000s, Sherman explained.

"That made it difficult for a lot of younger people to move out of the house, to get a job, to launch their own adulthood," he said.

However, that still doesn't explain why sexual behavior is down across all age groups and all adults. Future research efforts will attempt to puzzle out why this is happening —and what the consequences might be. Other studies have linked sex to psychological well-being, with people who have sex more frequently tending to report being happier, less depressed and less anxious. They are also less likely to suffer from psychological disorders, Sherman told Live Science.

"Of course, it's hard to determine where the causal arrow is pointing: Do I have more sex because I'm a happy person, or am I a happy person because I have more sex? It probably works both ways," Sherman said.

The findings were published online March 6 in the journal Archives of Sexual Behavior.

Original article on Live Science.