As a child growing up in Naarm/Melbourne, Sammie recalls spending a lot of time alone in her room, with the door locked.
Sammie — whose last name the ABC has agreed not to publish — lived in fear of setting off her older brother.
Warning: This story contains depictions of family violence
"Something we said wouldn't be right for him, and he'd start yelling, he'd start kicking up a fuss," Sammie told triple j hack.
"Then he'd break or smash things, that's when I was like, 'Okay, I need to go.'"
Sammie says the behaviour started when her brother – who's only 18 months older than her – was about eight or nine years old.
It would usually start as verbal abuse like yelling, before escalating to the destruction of property. Sometimes, Sammie says she or her mother would be physically assaulted.
"There was one time a screwdriver got thrown at me and I had to block my head [with my arm] so I've got a little scar on my elbow," Sammie said.
Sammie says she and her mum called the police many times, but she felt like an afterthought when they arrived at the family home.
"They didn't even really notice that I was there … They wouldn't even come and check on me."
Eventually, Sammie issued an ultimatum: either her brother left, or she did.
"I had to sit mum down and just say enough is enough."
Sammie's mum agreed to kick her brother out of the family home, and she says he then became homeless and started using illicit drugs.
Sammie doesn't have a relationship with him these days.
"If he stopped doing drugs, and he cleaned up himself, and he actually put the effort in to get better then, potentially, but I just don't see that ever happening," Sammie said about the prospect of rekindling a relationship.
"I don't even really see him as a brother anymore …. If he died, I really would not care."
More than sibling just rivalry
Hayley Boxall, a domestic violence researcher from the Australian National University, told hack that sibling to sibling domestic violence is more common than many assume.
"There are some international estimates which suggest that it is the most common form of domestic and family violence that is occurring within families," Dr Boxall said.
But despite its estimated prevalence, Dr Boxall says there's not much of an understanding about how this form of violence affects young people in Australia.
"We don't really have very clear criteria for what is sibling to sibling violence, as opposed to sibling rivalry and conflict," she said.
"So the short answer is, we really don't know [its prevalence], but we suspect that it is very, very common within families."
Dr Boxall and two colleagues decided to research by conducting a survey of young people.
The researchers defined sibling violence as behaviour that was persistent rather than episodic, had an intention to exert control, and had negative impacts on the victim.
Loading...The research, exclusively provided to triple j hack, found that emotional abuse was the most common form of sibling violence experienced by young people, with more than 70 per cent of survey respondents saying they had experienced that kind of behaviour.
"When we talk about emotional abuse [we mean] denigrating someone, calling them names, telling them that they're worthless … challenging their gender identity and sexual identity," Dr Boxall said.
Physical abuse was also very common, with nearly 65 per cent of respondents saying they'd been pushed, hit or had property damaged.
About 14 per cent of respondents had experienced non-fatal strangulation at the hands of a sibling, according to the research.
"We're really talking about a persistent pattern of behaviour that can include physical, non-physical and sexually abusive behaviours," Dr Boxall said.
'Learnt behaviour'
The research also found that there isn't a clear line between victim and perpetrator, with nearly one in five respondents saying they have been both the victim of sibling violence, and the perpetrator.
Dr Boxall said that's reflective of the complex family dynamics in households that use violence.
"A lot of these behaviours are learnt through the families that they're originating from. It can be intergenerational."
Nine out of 10 survey respondents who had experienced or perpetrated sibling violence said they had witnessed or experienced family violence with other family members.
The researchers say there also isn't as clear a gender divide with sibling domestic violence as with other forms of DV.
Hayley Boxall says there aren't many services for victims or perpetrators of sibling to sibling domestic violence. (triple j hack: Shalailah Medhora)
"A similar proportion of boys, girls and non-binary, trans young people said that they were both using and had been subjected to it," Dr Boxall said.
When the data was broken down to only young people who had experienced sibling violence and only people who had perpetrated it, Dr Boxall says her team's finding reflected more common trends.
"We do see this kind of gender divide there, where boys are more likely to use it, whereas women are more likely to be subjected to it," Dr Boxall said.
'Sense of betrayal'
The research found that the "impacts are often underestimated and minimised by family members and clinicians", due to the idea that they are simply a form of sibling rivalry.
The CEO of Relationships Australia NSW, Elisabeth Shaw, told hack that abuse by a sibling can bring up "a different sense of betrayal" from abuse perpetrated by others.
"With your siblings, you kind of expect that you'll hang in together," she said.
"When there's something abusive at your generational level, you can feel really alone, because they're meant to be your ally."
Ms Shaw also said perpetrators or other family members who minimise abuse as "rough play" or rivalry — or something kids will "grow out of" — can act to excuse the behaviour and deny victims an acknowledgement of the abuse.
Dr Boxall said experiencing abuse as a child can lead to dysfunctional or abusive relationships being normalised in adulthood.
"You've got those really transformative experiences in your family, when you experience abuse. It really affects your ability to trust other people and to form healthy loving bonds with other people. And that's why victims commonly go on to be re victimised later on in life," she said.
Ms Shaw said domestic violence services for young perpetrators are "few and far between".
"A lot of family therapists would be scared of working with this themselves, and they just they don't know what to make of it or how to deal with it. And sadly, parents are often pathologised as if they've lost control, and it's an issue of discipline and control, rather than looking at it as another form of abuse," she said.