Anecdotal mostly. Go to the skid row of your city and ask homeless people / prostitutes why they are where they are. You'll learn everything. Talk to them as if they are your brother or sister (even if you don't have one).
In terms of hard sauce, I've read numerous studies, watched documentaries, tons of people saying it. But mostly anecdotal.
Not saying all Monsters come out of the single-mother household, but most of them do, especially from the non-believing ones. Same way not all Believers come from a life-hood of going to Church. God favors who He wills, and punishes who He wills, Believer or not.