A disturbing study out by the Boston University School of Public Health has found that a surprisingly high number of teen girls ages 14-20 have had group sex.

Jezebel reports that of 328 girls who visited Boston-area health clinics 7.3% reported having group sex. What’s more disturbing is of that number the majority of the girls surveyed were “pressured, threatened, coerced, or forced” into the situation and 45% say that at least one male participant didn’t use a condom.

A third of the girls also said they used alcohol or drugs during their last group sex encounter and half of those were forced to imbibe by their partner.

“The average age of their first group-sex experience was 15.6 years old, and 54% of those studied had multi-person sex for the first time when they were younger than 16,” writes Jezebel’s Margaret Hartmann. “The age of consent is 16 in Massachusetts, so the majority of these young women had been raped.”

EurekAlert reports that 21% had more than one group sex experience but for the majority it was a one-time experience.

“Given the substantial proportion of girls who reported that their MPS (multi-partner sex) was nonconsensual, additional research to understand more about the perpetrators, and how to prevent this particular form of sexual violence, is warranted,” the study authors said.

The study showed that girls who reported having had group sex experiences were also more like to have been exposed to pornography in the last month, to “report cigarette smoking, dating violence,” or have been diagnosed with an STD.