This and other recent reviews of sibling relationships and influences (e.g., East, 2009
) support the view that levels of parenting warmth and negativity influence sibling relationships, and sibling dynamics affect parents and parenting. Moreover, PDT and the quality of sibling relationships impact children’s internalizing and externalizing behavior problems. And finally, siblings’ mutual reinforcement of antisocial attitudes and behaviors is a powerful additional influence on externalizing and substance use problems. In these many ways, siblings are a driving force in one’s competence and success at school, with peers, and with romantic partners, as well as one’s difficulties with self-esteem, depression, and disruptive, delinquent, and risky behavior. These effects extend from childhood into the rest of the life course.
Less is known about the macro social and economic contexts of sibling dynamics although progress is beginning to be made. Conger and colleagues’ Iowa study of families has implicated family economic stress in the quality of sibling relationships (e.g., Conger, Conger, Elder, Lorenz, & et al., 1992
), and Updegraff, McHale, Crouter and colleagues have begun to add to Brody and colleagues’ work on sibling relationships among non-white U.S. families (e.g., Brody et al., 2001
; McHale, Whiteman, Kim, & Crouter, 2003
; Updegraff et al., 2005
). Less work has been reported utilizing similar research approaches on sibling relationships in other countries, especially in non-white, non-European countries. The family contexts of sibling relationships deserve more emphasis (Eriksen & Jensen, 2009
): An important area for future work is greater understanding of the role of sibling relationships in families where child abuse or intimate partner violence exists. The questions include not only how siblings transmit such violence to each other, but also how they may buffer each other from negative effects of violence. Moreover, how do sibling relationships in such contexts affect the intergenerational transmission of violence?
The sibling context itself is another area where our understanding is not as thorough as it might be. For example, understanding of multiple sibling relationships has been lacking; most studies have stopped at two siblings. In addition, although studies of sibling relationships often do examine gender, gender composition, and birth order effects, the information is limited. A more comprehensive understanding of these factors in sibling relationships and sibling effects awaits a review devoted solely to this topic.
Although this article focused on sibling influences on mental and behavioral health problems, a better understanding of the positive role that siblings play in development is needed as well. Studies suggest that siblings can have positive influences on outcomes including social competence (Stormshak, Bellanti, Bierman et al., 1996
) and adaptive relationships skills (Updegraff et al., 2000
), but the processes underlying these associations have not been articulated and documented. Research on the benefits of sibling relationships could inform sibling-focused interventions and help to expand their goals to promoting positive outcomes in addition to reducing harmful sibling conflict and subsequent problem behaviors.
There is also room for progress in understanding sibling effects by conducting studies that are becoming more nuanced and methodologically sophisticated. Little work if any has focused on distinguishing among youth’s individual adjustment, sibling characteristics, and sibling relationship influences. Examining these will be difficult, as the three constructs (child characteristics, sibling characteristics, sibling relationships) are inter-correlated, and measuring the constructs in a manner that provides maximal distinctiveness requires considerable forethought. With the exception of a few notable lines of research, sibling investigation is often opportunistic—taking advantage of available datasets on families that are focused on other questions.
Although several of the best studies on siblings include longitudinal data, the use of experimental designs would provide information on causal processes regarding sibling effects. PDT is an area where causal questions remain open: To what extent are parents responding to differences in children vs. creating those differences? We hope that sibling-focused interventionists can take advantage of the experimental context provided in intervention trials to illuminate causal processes.
Given these questions and areas for future work, to what extent is our understanding of sibling relationships ready for translation into practice? We believe that there is sufficient evidence for clinicians to integrate a focus on siblings into child and family programs. For example, given the stress of sibling conflict on parents and the consequent undermining of positive parenting, parents should be introduced to effective ways to manage sibling disputes and ongoing sibling tensions. Parents also should be aware of the impact of their own harsh parenting and conflict with a partner on sibling relationships. When appropriate, the negative impact of sibling collusion and deviancy training should also be explained to parents, with support for monitoring and disrupting such processes.
Furthermore, clinicians should be alert to sibling influences: Children who are seen for mental and behavioral health problems may also be influencing, or influenced by, their siblings. For example, depressed children are likely irritable, prone to criticize, or provide low levels of support to siblings; depressed children may also be the victims of sibling bullying and abuse. Clinicians may inquire through interviews or questionnaires with parents, the target child, and siblings about sibling conflict and support as well as the perceived fairness of differential parenting. Where sibling processes are negative, additional treatment strategies (e.g., bringing siblings into the treatment process, providing additional strategies and support for parents) may be called for. Clinicians may also provide or recommend support for siblings who are coping with a family situation that includes not just a sibling’s problems but also reduced parental availability.
In these ways, we believe clinicians, researchers, and program developers may leverage the largely untapped potential of sibling relationships to promote more positive developmental outcomes.