The biggest bullies might not be in the playground, but in the top bunk.
That's the takeaway from a new study that says sibling torment could be more common than aggression at school or in the neighborhood — and the perpetrators and victims don't even see it as bullying.
"Rivalry is one word that they used," said Lori Hoetger, one of the University of Nebraska-Lincoln researchers who authored the study published in the Journal of Family Violence.
Her team questioned nearly 400 undergraduates about their experiences as children, using a checklist of physical and verbal behaviors that fit an academic definition of bullying if they are repeated over time.
To their surprise, the students reported bullying dynamics with brothers or sisters more often than with other peers. And those who had been bullied by a sibling were less likely to report someone else being harassed to an authority figure.
"We think that's because people who are experiencing sibling bullying somehow normalize it," Hoetger said.
Katey Smith, a licensed clinical social worker with the non-profit Family Centers in Connecticut, which provides mental health and parenting services to families, said that too often parents downplay home-base bullying.
But her current client list includes a mom and dad who recognized their older son, a gifted 11-year-old athlete, was picking on his artsy younger brother.
"It's verbal but it can become physical when rough play and wrestling turns into something more extreme," Smith said. "It's mostly the older brother making fun of the little brother. It’s all the time and it causes the little one quite a bit of stress because he looks up to his brother."
Smith is working with the parents on setting boundaries for the older boy and on coping mechanisms and emotional support for the younger one. It's crucial to break the cycle, she said, because bullying can have long-term effects.
A study last year by the University of New Hampshire found that the 32 percent of children who reported being victimized by a brother or sister suffered higher rates of mental-health distress. Researchers from Oxford University discovered children who were bullied by a sibling at age 12 were twice as likely to report depression or anxiety at age 18.
One criticism of the research comes from a surprising source. Ross Ellis, a real-estate agent who founded the non-profit advocacy group Stomp Out Bullying, said the friction is being overblown.
"This is sibling rivalry that started in ancient days and will continue in future days," she said. "Bullying is just the hot buzzword today."
But Dr. Gail Saltz, a New York psychiatrist who is a TODAY contributor, said that while old-fashioned rivalry may be the cause, there's no doubt it crosses the line in some households — and can spill over into the schoolyard.
"It's understood that kids who are bulliers at school are sometimes being bullied at home, often times by a sibling, though sometimes by a parent," she said. "And it has a sustained impact — depression, insecurity and loss of trust and intimacy in relationships."