New research published in the Journal of Sex & Marital Therapy suggests that polyamory, swinging and open relationships are more common in the United States than thought.

The study found that about one in five single Americans had engaged in some sort of non-monogamous relationship arrangement in their lifetime. The findings were based on two nationally representative samples of adults in the United States of America, which included a combined 8,718 people.

“While most people presume sexual commitment to one partner (sexual monogamy), some people have consensual agreements with their partners to engage in sex and/or romance with other partners,”

the study, led by Mara Haupert of Indiana University, said.

The study specifically examined the prevalence of consensual non-monogamy, which the researchers defined as “any relationship in which all partners agree that each may have romantic and/or sexual relationships with other partners.” Consensual non-monogamy includes polyamory, swinging and open relationships.

The study found 21.5 percent of individuals had been involved in a consensual sexually nonexclusive relationship at some point in their life.

Demographic traits such as age, education level, income status, religion, region, political affiliation, and race were not associated with consensual non-monogamy — suggesting that non-monogamous relationships are equally present across almost all strata of society. The findings show that “there is no single ‘type’ of person who engages in consensual non-monogamy,” the researchers said. However, gay, lesbian and bisexual individuals were slightly more likely to have engaged in a non-monogamous relationship than heterosexual individuals.

However, the researchers said their findings could be skewed because the study only included people who were currently single.