How many homeless youth in the U.S. are LGBT?

I always see different estimates, and never know what's what.

The question came up last week with news that a new plan from the Administration on reducing homelessness has sections specifically on homeless LGBT youth.

That Washington Blade article points to a January 2007 joint study by the National Gay and Lesbian Task Force and the National Coalition for the Homeless. That study surveyed the existing research and concluded that of an estimated 1.6 million homeless American youth, approximately 20-40 percent identify as LGBT.

Of course, research on homelessness is presumably hard to do; perhaps we shouldn't be expecting too exact a number.