To better understand the phenomenon, Dr. Martin conduced a literature review using Medline, Web of Sciences, PsycINFO, and Google Scholar. He identified 158 articles from peer-reviewed journals or textbooks.
Dr. Martin described sibling rivalry and sibling aggression and abuse separately, though overlap certainly occurs. Sibling rivalry – conflict over something the other sibling wants or a lack of balance between them – generally stems from resentment related to birth order and competition.
Common sources include favoritism or preferential treatment that one child perceives a parent to grant another sibling, problems with sharing possessions, and “fair” or “even” division of household chores.
“Usually the biggest problems is an impaired sibling relationship,” Dr. Martin wrote. But the experience can contribute to low self-esteem into adulthood if individuals believe themselves to be their parents’ less favored children, and sibling rivalry often can develop into sibling abuse.
Sibling aggression often is unrecognized with poor measures of prevalence, frequently relying on recall from college students. Yet, when paired with peer violence, sibling violence increases the likelihood of worse mental health outcomes, Dr. Martin found. Further, youth who fight with their siblings are 2.5 times more likely to fight with their peers.
The frequency of sibling violence is highest before age 9, but its “severity peaks in adolescence,” Dr. Martin wrote. Clinicians evaluating someone as a perpetrator or victim of sibling violence need to consider perception, intention, and severity in their assessments.
“Psychological aggression is often a precursor to physical aggression and often more damaging,” Dr. Martin wrote. Older siblings are more likely to be the aggressors, and males and females are equally likely to be victims and perpetrators of less severe abuse.
But “presence of a male child increases the likelihood of violence between siblings,” Dr. Martin found, and males are more likely to be perpetrators of more severe abuse – with one exception: Females are more likely to be perpetrators of sexual abuse. Although sexual abuse often is excluded from discussions of sibling violence, it is the most common form of familial sexual abuse.
Many psychological schools of thought can be used to explore causes from a theoretical perspective, but the list of interacting factors is long. It includes factors related to the parent-child relationship as well as individuals and the family as a whole.
Among the parent-child factors Dr. Martin lists are “parental differential treatment (particularly by fathers), active and direct judgmental comparison by parents, negative and conflictual parent-child relationships, lack of parental reinforcement of prosocial behavior, polarized definitions of good and bad children,” and rejecting or overcontrolling mothers. Other factors include coercive parenting, inadequate parental supervision, parental child abuse, parental approval of physical aggression between siblings, and lack of acknowledgment of children’s concerns.
In terms of the family unit, sibling violence is linked to domestic partner violence, marital conflict, poor family cohesion, living with a stepfamily, and lack of family resources and/or “lack of clear and consistent family rules,” Dr. Martin found.
While a “perpetrator’s lack of empathy, low self-esteem, and aggressive temperament” all are risk factors for sibling violence, protective factors include greater warmth in family relationships.
Sibling murder accounts for 1% of all homicide arrests and 8%-10% of all familial murders. The majority of these, about 75%, are brothers killing brothers. The remaining quarter include, in decreasing prevalence, brothers killing sisters, sisters killing brothers, and sisters killing sisters.
Though no evidence-based treatments exist for sibling violence, prevention strategies might include “secondary prevention, including family and individual approaches,” and “primary prevention with parenting programs for those at risk to abuse,” such as Successful Parenting, Systematic Training for Effective Parenting, and Parent Effectiveness Training.
Clinicians also have the option to modify existing tools, address sibling conflict through mediation, work to improve all family members’ communication skills, and establish rules for appropriate behaviors. Other treatment approaches may include “structured family therapy, task-centered approaches, utilizing social learning theory or nonviolent resistance,” Dr. Martin reported.