It’s a widely held belief that people who were abused as children are more likely to grow up to abuse their own children, but a new study in Science suggests a more complex picture. Different kinds of abuse and neglect have different patterns of intergenerational transmission, and there’s reason to think that certain families are scrutinized more than others, leading to biased reporting.

The widespread belief in intergenerational transmission is not completely unfounded. A number of studies have found evidence that abuse victims are more likely to abuse, but the overall picture is mixed: many other studies have found no such link. Understanding what causes child abuse is obviously vital to finding solutions, so it’s an essential question for researchers to resolve.

Part of the problem is that this is an incredibly difficult subject to study. Asking people to self-report their experience of abuse as children, or their tendency to abuse as adults, will obviously produce answers rife with inaccuracies. On the other hand, not all instances of abuse are reported officially and not all reported abuses have sufficient evidence to result in criminal charges.

A team of researchers at John Jay College of Criminal Justice constructed a new study design that tried to work around some of the main problems with obtaining data on child abuse. Previous research had used cross-sectional research, finding abusive parents and interviewing them about their childhood experiences. This means that people who were abused as children but who didn’t grow up to be abusers aren’t accounted for in the research. Past studies have also focused on physical abuse, ignoring sexual abuse and neglect.

To get around this problem, the John Jay researchers opted for a longitudinal study, identifying children who, based on official records, were known to have been abused or neglected between 1967 and 1971. They also identified a comparison group of children with no documented abuse or neglect cases, but who were from the same region and matched for age, sex, race, and social class.

Of course, there’s no guarantee that the children in the control group hadn’t also been abused or neglected without official reporting, but the controls do help to ensure that other social factors aren’t affecting the results.

The researchers first interviewed the study participants between 1989 and 1995 when they were around 29 years old. At this stage, there were 1,196 participants all together, although a number left the study before its conclusion. Analyses of those who dropped out indicate that there’s no reason to think that there were differences in abuse rates between those who stayed and those who left.

Follow-up interviews were conducted in 2009 and 2010, when participants were around 47 years old. The children of the participants—now young adults, 22 years old on average—were also interviewed at the same time. Finally, results were compared with reports from Child Protective Services (CPS).

They found that adults who had records of abuse or neglect as children were twice as likely to have been reported to CPS because of child maltreatment. Overall, approximately 21.4 percent of these adults had been reported, compared to 11.7 percent of those in the comparison group. Rates of reporting for sexual abuse and neglect were significantly higher, but reports of physical abuse were similar. This is a really important finding, because previous research and common assumptions have focused on physical abuse.

The second part of the study focused on self-reports. Parents in the abused group were no more likely to self-report behaviors that are considered abusive than control parents, but they were more likely to admit neglectful behaviors. But, write the authors, there’s reason to be skeptical of abusive parents’ willingness to report on their own behavior, so these reports might fall short of the truth.

The reports from the participants’ children portrayed a different picture. The children of parents who were abused were more likely to report sexual abuse and neglect than the children of parents with no abuse history, but no more likely to report physical abuse. This result matches with the data from CPS reports.

Finally, the researchers compared the self-reports of abuse with the rates of reporting to CPS, and they found something unexpected: CPS knew about more of the abuse and neglect cases in the abused group than they did in the control group. In fact, they knew about approximately 30 percent of the self-reported cases in the abused group and only 15 percent of cases in the control group.

The implication, the researchers suggest, is a surveillance bias toward families already involved with CPS. If CPS knows that there’s a history of abuse in a family, they watch them more closely and are more likely to know about ongoing abuse cases. This means that detection of intergenerational transmission of abuse based only on CPS records could be substantially skewed.

The researchers emphasize that there are weaknesses in this study despite its stronger design, and there’s a lot more work to be done. Apart from the obvious difficulties in obtaining complete and accurate reports of abuse, the families in this study were predominantly poverty-stricken, which means there’s an obvious confound with socioeconomic status. The results might not generalize to all socioeconomic groups.

What the results do suggest, though, is that CPS might be missing cases of abuse by focusing too much on families with a known abuse history. That’s an important avenue for future research to explore.

Science, 2015. DOI: 10.1126/science.1259917 (About DOIs).