Though several studies indicate that sibling abuse is far more common than other forms of family abuse, chronic maltreatment by siblings has only relatively recently become the subject of serious clinical study and concern. Sibling abuse is far less recognized than spousal or child abuse and is often considered less dangerous, although siblings who are a great deal larger and/or older than their younger counterparts may in fact be capable of lethal violence towards their victims.
Sibling abuse is significantly more likely to occur in dysfunctional, neglectful and/or abusive homes, and often reflects a lack of appropriate boundaries and discipline on the part of the parents. In many cases, sibling abuse can occur as "second hand abuse" in which children who have been harmed or maltreated go on to harm siblings. A 1982 study found that of 60% of children who witnessed their mothers abused by their fathers subsequently acted out the scene with their siblings. Similarly, those who witness abuse as children are more likely to abuse as adults: Malone and colleagues found that when children witnessed parental abuse they were more likely to behave abusively as adults, and that, contrary to common wisdom, girls from such families were more likely than boys to behave abusively towards partners as adults. The "Cinderella effect", which is a conventional wisdom in the Anglosphere, holds that sibling abuse is more common between half-siblings or full step-siblings than genetic siblings.
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According to many authorities and researchers, sibling abuse is one of the most common forms of abuse, yet it often remains to be neglected by society at large and by investigators into interpersonal violence:
- Vernon Wiehe of the University of Kentucky estimates that up to 53% of children have committed at least one act of severe aggression towards a sibling, making sibling abuse more common than child abuse by parents and spousal abuse combined.
- Hotaling, Straus, & Lincoln found that sibling aggression was somewhat common even in families that could not be classified as pervasively abusive, with 37% of 498 children committing at least one act of serious abuse during the previous year; in abusive families, 100% of children committed at least one act of serious abuse.
- Similarly, Whipple and Finton report that "Psychological maltreatment between siblings is one of the most common yet often underrecognized forms of child abuse."
- Irfan and Cowburn report that in Pakistani immigrant families in the UK, "Among perpetrators of abuse, 35% (highest proportion) of physical abuse was perpetrated by siblings, 33% by mothers and 19% by fathers."
- Several studies show that sisters are more likely to be victimized by brothers than vice versa. However, sisters can also abuse brothers, and traditional gender roles can allow such abuse to go unchecked: Schwartz and colleagues found that while women are more likely to use physical aggression during disagreements, parents are more likely to view male aggression more negatively than female aggression, even when the abusive acts are identical (e.g., boys throwing objects during a fight is seen as a more serious transgression than girls throwing objects during a fight). Similarly, Tyree and Malone report that women's violence as adults is more strongly correlated with aggression towards siblings during childhood.
- Caffaro, J. & Conn-Caffaro, A. (1998; 2005) report, based on their research, that adult sibling abuse survivors have much higher rates of emotional cutoff (39%) with brothers and sisters than what is evident in the general population (<6%)
Sibling sexual abuse
- Caffaro & Conn-Caffaro (1998; 2005) define sibling sexual abuse as sexual behavior between siblings for which the victim is not developmentally prepared, which is not transitory, and which does not reflect age-appropriate curiosity. It may or may not involve physical touching, coercion, or force.
- Bank and Kahn found that most sibling incest fell into one of two categories: "nurturance-oriented incest" and "power-oriented incest". The former is characterized by expressions of affection and love, while the latter is characterized by force and domination.
- Rudd and Herzberger report that brothers who committed incest were more likely to use force than fathers who commit incest (64% vs. 53%). Similarly, Cyr and colleagues found that about 70% of sibling incest involved sexual penetration, substantially higher than other forms of incest.
- Bass and colleagues write that "sibling incest occurs at a frequency that rivals and may even exceed other forms of incest," yet only 11% of studies into child sex abuse examined sibling perpetrators.
- Ryan writes how, "Child protection has focused on adult-child [sexual] relationships, yet we know that more than 40% of all juvenile-perpetrated child sexual abuse is perpetrated in sibling relationships."
- Rayment and Owen report that "compared the offending patterns of sibling offenders with other teenage sex offenders [...] Sibling abusers admitted to more sexual offences, had a longer offending history and a majority engaged in more intrusive sexual behaviour than other adolescent sex offenders. The sibling perpetrator has more access to the victim and exists within a structure of silence and guilt."
- A survey of eight hundred college students reported by David Finkelhor in Journal of Marriage and Family Counseling found that fifteen percent of females and ten percent of males had been sexually abused by a sibling.
Sibling abuse vs. sibling rivalry
"As a rule, parents and society expect fights and aggression among siblings. Because of this, parents often don’t see sibling abuse as a problem until serious harm occurs."
Sibling rivalry, competition and disagreements are considered a normal component of childhood and adolescence. Weihe suggests that four criteria should be used to determine if questionable behavior is rivalry or abusive. First, one must determine if the questionable behavior is age appropriate, since children use different conflict-resolution tactics during various developmental stages. Second, one must determine if the behavior is an isolated incident or part of an enduring pattern: abuse is, by definition, a long-term pattern rather than occasional disagreements. Third, one must determine if there is an "aspect of victimization" to the behavior: rivalry tends to be incident-specific, reciprocal and obvious to others, while abuse is characterized by secrecy and an imbalance of power. Fourth, one must determine the goal of the questionable behavior: the goal of abuse tends to be embarrassment or domination of the victim.
Signs of abuse
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- One child always avoids their sibling
- A child has changes in behavior, sleep patterns, eating habits, or has nightmares
- A child acts out abuse in play
- A child acts out sexually in inappropriate ways
- The children’s roles are rigid: one child is always the aggressor, the other, the victim
- The roughness or violence between siblings is increasing over time 
Systemic Risk and Protective Factors Associated with Sibling Abuse
- Parental unavailability and lack of adequate supervision of children in the home
- Attachment difficulties in which parents may be physically available but emotionally absent
- Ineffective parenting
- Low levels of parental acceptance and involvement linked to higher levels of sibling conflict
- Parental favoritism
- Sibling relations characterized by power imbalances, role rigidity, and unclear boundaries
- Consistent disregard for siblings' personal and psychological space
- Families with distressed marriages and high levels of parent-child and spousal conflict
- Relationship between family functioning and larger ecosystem factors such as sexism in society or pornography
- Father's level of positive involvement with sons closely associated with stability of sibling behavioral problems
- Quality of mother-child interaction mediating effects of overt martial conflict on older siblings' tendency to behave aggressively
- Parental warmth and involved interactions; consistent, nonpunitive discipline management
- Affectional ties with alternative caregivers including grandparents and older siblings
- Presence and ability to make use of community support systems (i.e., neighbors, teachers, friends)
- Parents learning to create balance between overinvolvement in siblings' affairs and a lack of protective, competent parenting
The 1991 made-for-TV movie "My Son, Johnny" is a rare fictionalized portrayal of sibling abuse. The film stars Corin Nemec as a teenager victimized by his older brother played by Rick Schroder. The film was inspired by the real-life case of Philadelphia fifteen-year-old Michael Lombardo, tried and acquitted for the 1985 killing his nineteen-year-old brother Francis "Frankie" Lombardo who had battered and abused him for years.
British soap opera, Brookside, ran 1996 a controversial storyline in 1996, featuring incest between siblings Nat and Georgia Simpson that ended in pregnancy followed by an abortion. The sympathetic portrayal of the situation attracted criticism from commentators such as Peter Hitchens (in his book The Abolition of Britain).
Canadian animated series Total Drama Pahkitew Island, the second half of the fifth season of Total Drama, brings in Amy and Samey, the show's first twin sibling pair. Amy is the mean twin, while Samey (who prefers to be "Sammy") is the nice twin who has to deal with Amy's abuse towards her.
Notable examples of sibling abuse
Cheyenne Brando, the daughter of the legendary actor Marlon Brando, confessed that her brother Christian Brando seemed to be in love with her and that he was jealous of her boyfriend Dag Drollet; that is why Christian killed him in 1990, according to Cheyenne. Christian stated during his trial that Cheyenne told him that Dag was abusive to her, that he wanted to protect her and that he never meant to kill Dag; it was a terrible accident. Christian was sentenced to ten years in jail in 1991 and Cheyenne committed suicide in 1995. Cheyenne was abusive with her two sisters, Maimiti and Raiatua, as well as with Marlon Brando, and Tarita, her parents, particularly her mother. Tarita Teriipaia wrote a book in 2005, which revealed Cheyenne terrorized her own family when she started to suffer from schizophrenia.
The son of the French politician Philippe de Villiers, Laurent, filed a complaint in 2010 against his elder brother, Guillaume, for having raped him when he was ten to thirteen. De Villiers always wanted to cover up the case and reproached his son about the charges against his brother by saying, "Your brother will go to jail because of you, is this what you want?!" He even managed to persuade Laurent to withdraw the complaint, but then he lodged it again. Finally the case was dismissed even though Laurent has got evidence of the abuse. Laurent wrote a charitable book, "Tais-toi et Pardonne" ("Be silent and forgive"), in which he said that his brother, six years his senior, also used to hit him. He also said that his parents knew about this and the incest, but always denied and ignored it. This case also explores the responsibilities of the parents in preventing abuse.
In 2013, Sylvester Stallone was accused by his late half-sister of physical and sexual abuse. What happened will never be known for sure, but in any case there was sibling abuse: either Stallone abused her, as well as their mother Jacqueline, who denied the abuse, or his sister abused him by blackmailing and financially abusing him and reflecting on his integrity by attempting to report false charges.
The Australian actor Hugh Jackman opened up the physical and verbal abuse of his older brother in 2013. He said that this abuse helped him for his acting in Wolverine and when his brother apologized, Jackman felt released.
The late Playboy Playmate and actress Anna Nicole Smith stated to a journalist few times before her demise that she was not only physically and sexually abused as a child by her stepfather but also by her brother and her sister. And her mother psychologically abused her by letting them abuse her. These accusations of abuse have not been proven.
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- Straus, M. & Gelles, R. (1990). Physical violence in American families: Risk factors and adaptations to violence in 8, 145 families. New Brunswick, NJ: Transaction Books.
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- University of Michigan Health System: Sibling abuse
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- Time Magazine: Reluctant Referees
- Cyr, M., Wright, J., McDuff, P., & Perron, A. (2002). Intrafamilial sexual abuse: Brother-sister incest does not differ from father-daughter and stepfather-stepdaughter incest. Child Abuse and Neglect, 26, p. 957-973.
- Laviola, M. (1992). Effects of older brother-younger sister incest: A study of the dynamics of 17 cases. Child Abuse and Neglect, 16, p. 409-421.
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- Disciplining, Chastisement and Physical Child Abuse: Perceptions and Attitudes of the British Pakistani Community
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- Ryan, G. (2005) Preventing Violence and Trauma in the Next Generation. J Interpers Violence 2005; 20; 132 doi:10.1177/0886260504268605
- S. Rayment and N Owen. (1999) WORKING WITH INDIVIDUALS AND FAMILIES WHERE SIBLING INCEST HAS OCCURRED: THE DYNAMICS, DILEMMAS AND PRACTICE IMPLICATIONS. Paper presented at the Children and Crime: Victims and Offenders Conference convened by the Australian Institute of Criminology and held in Brisbane, 17–18 June 1999
- Finkelhor, D. (1978). Psychological, cultural, and family factors in incest and family sexual abuse. Journal of Marriage and Family Counseling, 4, 41-79.
- Wiehe, V. R. (1997) Sibling abuse: Hidden physical, emotional, and sexual trauma, 2nd edition. Thousand Oaks, CA: Sage Publications, Inc.
- Caffaro, J.V. (2013). Sibling Abuse Trauma, 2nd Edition. NY: Routledge
- IMDB page
- Hitchens, Peter (2000). The Abolition of Britain. Quartet Books; New edition (1 April 2000). ISBN 0-7043-8140-0.
- "1990-2004: "Brando's Affair", Family drama and Death of Marlon. Part 1".
- "Court dismisses rape claim between French MEP's sons".
- "Laurent de Villiers raconte ce que lui a fait subir son frère". Retrieved May 23, 2013.
- "French court rejects rape claim between politician's sons".
- "Secret tapes of Sylvester Stallone and his half-sister 'destroyed as part of abuse payout deal'".
- "Guy Georges".
- "Hugh Jackman: "My wife and my kids are the real centre of my world"".
- "Hugh Jackman : Fils abandonné et frère tyrannisé, il est devenu Wolverine !".
- "Hugh Jackman: 'What are ya – a poof?'".
- "Bullied Jackman wanted to ‘kill’ brother".
- "The Tragedy Of Anna Nicole Smith".
- Wiehe, Vernon R. What Parents Need to Know About Sibling Abuse: Breaking the Cycle of Violence (2002)
- Caffaro., J. & Conn-Caffaro, A. (1998). Sibling Abuse Trauma, NY: Routledge.
- Caffaro, J. & Conn-Caffaro, A. (2005). Treating Sibling Abuse Families. Aggression & Violent Behavior, 10(5), 604-623.
- Caffaro, J. (2013). Sibling abuse trauma. 2nd Edition. NY: Routledge.