It might not be possible to answer this question. The 1/3 value might be accurate, but it isn't, and can't be, precise.
Psychology Today says:
Among youth who identify as sexual minorities, the likelihood of death by suicide has been estimated to be two to seven times greater than the likelihood of death by suicide among heterosexual youth (Haas et al., 2011). Haas et al. suggest that such a range exists because records of death rarely include a person’s sexual orientation.
Even it the 1/3 value were correct, it would still be meaningless without knowing the percentage of gay/straight teens. What if 50% of teens experience homosexual feelings at some time — the 1/3 would mean gays are less likely to kill themselves.
Much more reliable statistics are known however for suicide attempts (as the cause is usually determined during treatment).
And the incidence of attempted suicide is a lot more useful measure of the underlying problem than the incidence of actual suicide.
The "Trevor Project" knows a lot about attempted suicides:
Founded in 1998 by the creators of the Academy Award®-winning short film TREVOR, The Trevor Project is the leading national organization providing crisis intervention and suicide prevention services to lesbian, gay, bisexual, transgender, queer & questioning (LGBTQ) young people under 25.
Their facts about suicide page has a lot of statistics and references:
- Suicide is the 2nd leading cause of death among young people ages 10 to 24.[A]
- LGB youth seriously contemplate suicide at almost three times the rate of heterosexual youth.[B]
- LGB youth are almost five times as likely to have attempted suicide compared to heterosexual youth.[B]
- Of all the suicide attempts made by youth, LGB youth suicide attempts were almost five times as likely to require medical treatment than those of heterosexual youth.[B]
- Suicide attempts by LGB youth and questioning youth are 4 to 6 times more likely to result in injury, poisoning, or overdose that requires treatment from a doctor or nurse, compared to their straight peers.[B]
- In a national study, 40% of transgender adults reported having made a suicide attempt. 92% of these individuals reported having attempted suicide before the age of 25.[C]
- LGB youth who come from highly rejecting families are 8.4 times as likely to have attempted suicide as LGB peers who reported no or low levels of family rejection.[D]
- 1 out of 6 students nationwide (grades 9–12) seriously considered suicide in the past year.[E]
- Each episode of LGBT victimization, such as physical or verbal harassment or abuse, increases the likelihood of self-harming behavior by 2.5 times on average.[F]
SOURCES:
[A] CDC, NCIPC. Web-based Injury Statistics Query and Reporting System (WISQARS) [online]. (2010) {2013 Aug. 1}. Available from:www.cdc.gov/ncipc/wisqars.
[B] CDC. (2016). Sexual Identity, Sex of Sexual Contacts, and Health-Risk Behaviors Among Students in Grades 9-12: Youth Risk Behavior Surveillance. Atlanta, GA: U.S. Department of Health and Human Services.
[C] James, S. E., Herman, J. L., Rankin, S., Keisling, M., Mottet, L., & Anafi, M. (2016). The Report of the 2015 U.S. Transgender Survey. Washington, DC: National Center for Transgender Equality.
[D] Family Acceptance Project™. (2009). Family rejection as a predictor of negative health outcomes in white and Latino lesbian, gay, and bisexual young adults. Pediatrics. 123(1), 346-52.
[E] CDC. (2016). Sexual Identity, Sex of Sexual Contacts, and Health-Risk Behaviors Among Students in Grades 9-12: Youth Risk Behavior Surveillance. Atlanta, GA: U.S. Department of Health and Human Services.
[F] IMPACT. (2010). Mental health disorders, psychological distress, and suicidality in a diverse sample of lesbian, gay, bisexual, and transgender youths. American Journal of Public Health. 100(12), 2426-32.
