Yes this is true of any mental health issue in any population, we can only rely on self-reporting. If you have any sources that show "almost all" homeless people in SF are mentally ill, I'd be interested to read them.
From what I've read, at the national level the incidence of serious mental illness in the homeless population are around 20 - 25%. So the numbers for San Francisco seem reasonable.
From what I've read, at the national level the incidence of serious mental illness in the homeless population are around 20 - 25%. So the numbers for San Francisco seem reasonable.