A survey by the poverty program firm Maximus in New Orleans studied food stamp families, both the women receiving food stamps for their children and the men who fathered the kids. This was a study of poor families, but since 80% were black (at a time, pre-Katrina, when the city was 67% black), this is mostly a study of poor black families. Indeed, this is a good picture of some of the worst-off black families in the whole country -- poor, unmarried parents, who were poor even in a poor city in a poor state.
Ronald Mincy and Hillard Pouncy, two veteran black family researchers, analyzed the data hoping to find a "magic moment" when policy makers could promote marriage. What they discovered, though, was that most of the relationships were over even before the child was born. 70% of the women already had a child before the focal child of the study, and half of the fathers of child #1 were not the same as the father of child #2. Not surprisingly, the more children a man had by different women, the less he was likely to invest in any of them. Somewhat surprisingly, men with part-time jobs were less likely than men with full-time jobs to have their children stay with them even sometimes; it is likely, though, that the part-timers are living with other women, possibly with other children, and don't want his other kids in the house.
The main reason that the couples gave for not marrying was that they didn't have enough money -- though most of the women, and nearly all of the men, were working (sometimes under the table). Probing further into why the parents didn't marry, 2/3rds of the women and (somewhat surprisingly) 2/3rds of the men said they didn't think the other parent would be faithful.
Without marriage, half the men had drifted into a sometime involvement with their child, and another quarter had disappeared altogether. Even the "involved fathers" thought "supporting their children" meant giving money and gifts sometimes, on an irregular and informal schedule.
This study of the poor of pre-Katrina New Orleans is just one case study. It does, though, give us some baseline numbers of how bad the family situation is of the worst-off black families in America.