I am really confused as to how your personal experience would ever be able to figure out the actual percentage of homeless people who suffer from mental illness/drug addiction. No amount of experience would tell you those percentages, because no experience would have you meeting with a uniform sample of the homeless. Your experience is always going to have a huge selection bias.
It takes rigorous research, with properly accounted for selection biases, to determine actual ratios of the population as a whole.
It takes rigorous research, with properly accounted for selection biases, to determine actual ratios of the population as a whole.