LAWRENCE — Sibling aggression takes many forms, like hitting, shoving, threatening or calling names. Although sibling aggression is widespread and can shape people for years, it hasn't been studied well by psychological researchers.
"It's been understudied because we just think that it's normal," said Paula Fite, chair and Dean's Professor of Clinical Child Psychology at the University of Kansas. "The attitude is, 'Siblings are going to fight, and they're not always going to get along, and it's just a rite of passage.'"
Now, Fite and co-authors have just published an investigation into sibling aggression in the Journal of Psychopathology and Behavioral Assessment, based on data from 290 elementary-school children with siblings. The researchers found roughly 1 in 6 children reported using or threatening physical force to dominate a sibling, while about 1 in 8 said they had threatened or bullied a sibling to get something.
A key takeaway is that parents should take aggression between siblings seriously, even when it seems more like everyday family squabbling, Fite said.
"Maybe parents see the sibling stuff as normative — but if their kids did that same thing with a peer, parents would feel like they need to do something about it," Fite said. "But we actually compared the rates, and sibling aggression is much higher than peer aggression."
The researchers classified sibling aggression into two overarching types: "proactive," where one sibling is aggressive toward another without provocation, and "reactive," where a sibling is provoked into aggression as retribution.
"We see that reactive aggression is more common with siblings as well as peers, and part of that, we think, is emotion regulation and trying to build up those skills," Fite said. "Reactive aggression is going to be more socially acceptable, that you did it in retaliation as opposed to you did this in some sort of cold-blooded, calculated way."
Fite's collaborators were lead author Charlsie Solano and Kat Lell Wright, both of whom are clinical child psychology graduate students at KU; and Cara Swit, an associate professor in the School of Health Sciences at the University of Canterbury in Christchurch, New Zealand.
Among their other points, the researchers emphasize that both functions of sibling aggression can have negative results later in life.
"Distinguishing between those subtypes of aggression better predicts outcomes," Fite said. "Reactive aggression is associated with feeling bad afterward, and a lot of kids who exhibit reactive aggression demonstrate depression and anxiety symptoms. Whereas proactive aggression is more strongly linked to delinquency and substance abuse, in the sense of binge drinking and risk-taking."
Moreover, aggression between siblings can spill outside the family dynamic. The researchers found both subtypes of sibling aggression are linked to peer aggression six months later.
"It's certainly related to following aggressive patterns, that you take those same patterns of behavior in the sibling relationship, and that does influence your peer relationships," said the KU researcher. "We know it's important to address among siblings, not just wait until they exhibit those problems with peers."
Perhaps surprisingly, the research team found no difference in reported instances of sibling aggression between boys and girls.
"Once you get outside of the family environment, then you see where boys will be more physically aggressive, specifically," Fite said. "But we don't see necessarily within the sibling relationships those gender differences."
Fite said parents should be mindful of repeated aggressive behavior between siblings, including teasing.
"If you talk to some siblings, they'll say that what hurt them the most as a kid is their sibling saying mean things about them, and that can have long-lasting impact," she said. "So I think for parents, it's important to look at the patterns and have that open dialogue and communication. But just to ignore or tell them to figure it out, sometimes they don't have the skills to do that, and they need the instruction and someone to explain to them how to do that."
Fite said many questions remain about sibling aggression and the developmental trajectories of siblings involved in patterns of proactive and reactive aggression.
"I would love to follow the same kids and see how those peer dynamics play out, and then how that's related to more delinquent behaviors," she said. "That includes early substance abuse and problem behaviors. I'd be interested in understanding, for both the aggressors and the victims, who they partner with as far as peer relationships, and what those turn out to be like."
