Overall, American adults are having less sex than they did a quarter century ago, with married people showing the most dramatic decline of all.

The paper, published in the journal Archives of Sexual Behavior, showed a drop across gender, race, region, education level, and work status. One factor is the higher percentage now of unpartnered people, who tend to have less sex than partnered ones. But a major driver is a steady fall in the rate of sexual activity for people who are married or living with partners, which reduces what had been known as the “marriage advantage.”

Using 1989-2014 data from the General Social Survey, the study found that American adults have sex seven to nine fewer times per year than in the 1990s. Back then, the average person had sex 60 to 62 times a year, but in the early 2000s the frequency began to slip, and by 2014 it had declined to less than 53 times a year.

When looking only at married people, the drop was even sharper – from around 73 times a year in 1990 to around 55 in 2014 – bringing their frequency of sexual activity below that of never-married people. People in that group have sex an average of 59 times a year.