A new study estimates that 83 percent of gay male youth athletes in the United States are keeping their sexual orientation hidden from some or all of their teammates. Lesbian athletes in the same age group (under 22 years old) were more willing to be public about it — 63 percent said they were hiding their orientation.

The reason for the secrecy — even in an age when polls show that acceptance has been increasing — is often fear. Nearly half of gay men and 44 percent of lesbians around the world who kept their sexual orientation hidden said they did so in order not to be bullied. In addition, fear of discrimination from coaches or officials was mentioned by 32 percent of gay men and 28 percent of lesbians.

The survey found that 80 percent of the respondents, both gay and heterosexual, had witnessed or experienced homophobia in sports.

Titled “Out On The Fields,” the report was based on a survey of nearly 9,500 gay, bisexual and heterosexual people and claims to be the largest-ever study on homophobia in sports. (The questions only related to sexual orientation, not gender identity, so the study offers no information about transgender athletes.)

After publicizing the anonymous online questionnaire through various media outlets, the researchers received answers from several English-speaking countries. The highest numbers of responses came from Australia (3,006), the United States (2,064), the United Kingdom (1,796), Canada (1,123), New Zealand (631) and Ireland (501).

The United States received the lowest overall “inclusion score” of all the countries analyzed, with a high number of respondents saying the U.S. was not accepting of gay athletes. (Though because of the small sample sizes for respondents from New Zealand and Ireland, it isn’t necessarily fair to say that the U.S. ranks worst.)

In a phone interview, the survey’s lead author, Erik Denison, said attitudes about privacy among athletes are often related to the perception of homophobia in sports.

“I made that decision myself when I kept in the closet,” he said. “Implicitly it is about discrimination, though. The straight men can talk openly in conversations about what you did at the weekend, the women they met. If you’re gay though, you either have to make up stories or be excluded. It’s not the same.”

The large scale of the survey, though, doesn’t mean that it is the definitive word on homophobia in sports. Even in countries that had a high number of respondents, it can be difficult to tease out more detailed trends because the subgroups are far too small. Responses were split into youth and adult sports (i.e. under age 22 and over age 22) but also broken out by sports played and the sexual orientation of the respondents.

What’s more, not everyone even said they played sports — among U.S. respondents, for example, 81 percent of gay women and 75 percent of gay men said they participated in youth sports, while 63 percent of gay women and 42 percent of gay men said they participated in adult sports. As a result, the finding that 83 percent of gay male youth athletes keep their sexuality hidden from teammates is based on just 114 individuals.

Denison and his co-author, Alistair Kitchen, both members of Australia’s first gay rugby team, said they were are aware of those limitations. Their international approach was partly informed by the fact that past smaller-scale studies on homophobia in sport have been dismissed for being too limited in scope. The final methodology and findings were reviewed by seven academic experts prior to publication.

Overall, these results should be treated as estimates in an under-researched area filled with speculation, rather than definitive numbers about gay athletes.

Gay respondents were more likely than heterosexual ones to say that homophobia was more common in team sporting environments than in general society. But LGB athletes also related positive reactions to revealing their orientation to their teammates. In its write-up of the report, the gay sports site Outsports.com acknowledged many of the issues cited by respondents but added that “people in sports behave very differently when an athlete actually comes out,” often welcoming the LGB athlete and apologizing for language used in the past.

Denison also described what he called “the snowball effect” — the notion that the more LGB athletes there are who are open about their sexual orientation, the more accepted gay athletes will become in sports. As evidence for that, Denison pointed to the higher share of lesbian athletes in the U.S. who are open about their sexuality with their teammates and the fact that lesbian athletes around the world are more likely to say teams offer them a “supportive and safe environment.”

Because of their visibility, LGB professional athletes are likely more influential than amateurs in getting the snowball effect rolling, but few seem comfortable speaking publicly. The survey allowed respondents to submit detailed stories about themselves — around 1,600 did so. Denison said that about three dozen of those who provided narrative accounts were professional athletes, including at least two on their respective countries’ national teams.

Last year, after the professional football player Michael Sam told ESPN and The New York Times that he is gay, he said he received messages from many fellow athletes who “had the courage to tell me that they were also gay, but they do not have the same courage as I do to come out.”

So far, Sam’s decision has not created a snowball effect in the U.S. — partly because there will need to be other outspoken gay athletes before the sport reaches what Denison describes as “a critical mass.”