Teenage girls attack other girls because they are "acting like sluts" and threatening the perpetrators' relationships with males, concludes a new five-year Canadian study.

The University of Victoria results reveal that these attacks, observed over long periods of time in 16 Vancouver Island schools, are justified because the victims "caused" and "deserved" them.

"Violence is wrong and I never beat up a girl who wasn't asking for it," one participant said in the study by Sibylle Artz, the university's director of the school of child and youth care.

The research will be presented at one of the first-ever international conferences on girlhood aggression, which gets underway today in Toronto. Other new studies being unveiled will include a paper on how girl bullies have problems with romantic relationships later in life.

"Her work is groundbreaking and is contributing enormously to our understanding of delinquent and violent girls," Marissa Michel, a researcher at Toronto's Earlscourt Child and Family Centre, said of Dr. Artz's work on female violence among youth.

"We're just at the beginning of trying to understand girls who are growing up angry, aggressive and anti-social," said Kathy Levene, the centre's clinical director. "There is so little written and known about girlhood aggression, particularly among young girls."

Ms. Levene will present new detailed data on troubled girls aged 7-12, who have been treated for aggression, and their families. Early indicators from the study suggest that the young girls began to have medical problems as infants, had difficult temperaments and did not show affection as babies. "They were not warm and cuddly," she said.

The research suggests that problem girls were controlling from an early age and were always stubborn and self-centred. The children tended to come from difficult family environments and often faced various forms of abuse.

They were part of a highly problematic, usually difficult, mother-daughter relationship where they yelled at their mothers and often hit them. They had trouble in school and were socially rejected by other girls, often isolated and usually bullied, she added.

Dr. Debra Pepler, an international bullying expert in the psychology department at York University, will be on hand to present her latest findings after observing young girls, in Grades 1-6, socializing in their playgrounds at four different elementary schools.

"When we observe girls bullying on the school playground, about half the time their targets are boys. So what looks like a type of pre-courtship or attention-seeking behaviour may actually establish patterns that lead to problems in romantic relationships later on."

Dr. Pepler's research is among the first in its field, she said, because "Girls tend to be less physically aggressive than boys and they aren't knocking down old ladies and swarming around in gangs, so often we think everything is fine. But we have overlooked the problems that girls have and that's why we're having this conference."