US adults are today having sex less often than they did in the 1990s and it is not because of their busier lives, says a study.
In fact, the researchers found that those who worked more hours actually had sex more often.
Blame might be placed on the busy lives of more working parents, but the research did not bear that out, said the study's lead author Jean Twenge, Professor at San Diego State University in the US.
According to the study published in the journal Archives of Sexual Behavior, Americans had sex about nine fewer times per year in 2010-2014 compared to 1995-1999.
The study is based on data collected from the General Social Survey, a nationally representative sample of more than 26 000 American adults asked about their sexual behaviour since 1989.
"These data show a major reversal from previous decades in terms of marriage and sex," Twenge said.
"In the 1990s, married people had sex more times per year than never-married people, but by the mid-2000s that reversed, with the never-married having more sex," Twenge said.
A critical factor appears to be birth cohort, with later-born generations having sex less often than those born earlier in the 20th century, Twenge said.
Age also appears to play a significant role.
People in their 20s have sex more than 80 times per year, declining to 60 times per year by age 45, and 20 times per year by age 65.
Each year after the peak of sexual frequency at 25, sexual frequency declines 3.2 percent, the researchers pointed out.
"Older and married people are having sex less often – especially after 2000," Twenge said.
"In a previous paper, we found that the happiness of adults over age 30 declined between 2000 and 2014. With less sex and less happiness, it's no wonder that American adults seem deeply dissatisfied these days," Twenge said.