Frankly, I'm surprized that this is seemingly the first mention of this...
"The Suicide Prevention Resource Center synthesized these studies and estimated that between 30 and 40% of LGBT youth, depending on age and sex groups, have attempted suicide."
I went to the website of the organization you mentioned. I browsed and then searched that website. A link there took me to another organization, the American Association of Suicidology, at first to a dead link, then I browsed and searched that organization's website, and found a fact sheet on the issue you bring up.[1] The fact sheet mentions some studies and their conclusions, without detailed citations or descriptions of methodology, and points out "Because no reliable data exists, we do not know whether LGBT youth die by suicide more frequently than their straight peers. Sexual orientation and gender identity data are not included on death certificates so aggregated national death data do not include this information. In addition, many LGBT youth do not disclose this information to family members and friends; as a result, sexual orientation and gender identity often do not show up in psychological autopsy interviews." In other words, we are not completely sure that LGBT status is a risk factor for completed suicide in the United States, although that is the current working hypothesis among many suicide researchers. As the article submitted to open the thread here today makes clear, there is a lot of basis research on suicide that still needs to be done.
"The Suicide Prevention Resource Center synthesized these studies and estimated that between 30 and 40% of LGBT youth, depending on age and sex groups, have attempted suicide."
Source: http://en.m.wikipedia.org/wiki/Suicide_among_LGBT_youth
I hope I just missed the reference somewhere in the piece or these comments.