ReviewHow can adolescent aggression be reduced? A multi-level meta-analysis
Introduction
Aggression among adolescents is a worldwide problem. For example, Craig et al. (2009) found that bullying is common in 40 countries across Europe and America. In the United States, Lynne-Landsman, Graber, Nichols, and Botvin (2011) found aggression increases through adolescence, with 51% of their sample presenting high levels of aggressive behaviour at the end of middle school. Aggressive behaviours during adolescence are associated with negative immediate and long-term outcomes for both victims and perpetrators. For example, victims of bullying have more mental health problems during adulthood than those who have not been bullied (Arsenault, 2017) and adolescents who display aggression are more likely to have drug problems, present depressive symptoms and be arrested as an adult (Hyde, Burt, Shaw, Donnellan, & Forbes, 2015; Rhoades, Leve, Eddy, & Chamberlain, 2016). In the US alone, the annual cost of serious aggression among adolescents is over $21 billion (National Center for Injury Prevention and Control (U.S.). Division of Violence Prevention, 2019).
Many interventions have been developed to prevent and reduce aggressive behaviour in adolescents. Previous reviews have concluded that these interventions are effective (see Appendix A for an overview of 38 previous systematic reviews and meta-analyses including adolescents). However, it is still not clear which specific characteristics and techniques included in these interventions are most effective among adolescents. Only six of these reviews have investigated what works specifically in adolescents: two meta-analyses and four systematic reviews. The meta-analyses have focused on specific interventions involving sports participation (Spruit, Assink, van Vugt, van der Put, and Stams, 2016) and positive youth development (Melendez-Torres et al., 2016), and although the systematic reviews included a broader range of interventions, they did not quantify their effects (Cox et al., 2016; Gavine, Donnelly, & Williams, 2016; Kelly, 2017; Limbos et al., 2007). Therefore, a meta-analysis that identifies what works to reduce aggression in adolescents is currently unavailable.
Despite the limitations of the previous systematic reviews, some have suggested that interventions aimed at those at greater risk of perpetrating aggression (i.e., targeted interventions) may be more effective than interventions aimed at the general adolescent population (i.e., universal interventions; Gavine et al., 2016; Limbos et al., 2007). The mechanisms underlying effectiveness in universal and targeted interventions might also be different and many reviews focused solely on universal or targeted interventions (see Appendix A). This is important because numerous reviews have concluded that behaviour training and social skills training are the most effective components of interventions that are targeted rather than universal (Fossum, Handegård, Martinussen, & Mørch, 2008; Molina, Dulmus, & Sowers, 2005; Mytton, DiGuiseppi, Gough, Taylor, & Logan, 2006; Özabacı, 2011; Wilson & Lipsey, 2007). Identifying which intervention components are effective in improving behaviour is valuable in guiding intervention optimisation. However, without a common language, it is difficult to describe and compare intervention components. For example, Wilson and Lipsey (2007) defined “behavioural strategies” as giving rewards and incentives, whereas Özabacı, 2011 characterised learning and practising behavioural responses as “behavioural strategies”. This limitation can be overcome by using a common framework or taxonomy. The present meta-analysis will use the Behaviour Change Technique (BCT) taxonomy version 1 (Michie et al., 2013) to identify the BCTs included in interventions and test which are effective in reducing aggression among adolescents. We will also test whether BCT effectiveness differs between universal and targeted interventions. The BCT taxonomy has been widely used to analyse interventions addressing many health behaviours such as diabetes care (Presseau et al., 2015) and physical activity (Cradock et al., 2017). The taxonomy includes 93 techniques such as feedback on behaviour, problem solving and adding objects to the environment that aim to change behaviour.
Duration is another characteristic that previous reviews focusing on adolescents have found as a significant moderator of effectiveness. Limbos et al. (2007) suggested in their systematic review that interventions that lasted 12 months or more were more likely to be effective than shorter interventions. However, other reviews have found that longer interventions are not more effective than shorter ones (Fagan & Catalano, 2013).
Systematic reviews and meta-analyses of interventions to reduce aggressive behaviour across children, adolescents and adults have suggested that the existence of other factors in addition to targeting and duration that might moderate intervention effectiveness. However, they have not considered adolescents as a group separate from children and/or adults. Therefore, there is a need to investigate whether these factors moderate the effect of interventions in adolescents as it is possible that interventions need to be specifically tailored for this target group (Yeager, Dahl, & Dweck, 2018).
One of the factors that might moderate the effectiveness of interventions to reduce aggression in adolescents is whether intervention is delivered individually or to a group. Group interventions have been found to be less effective with samples containing high proportions of boys (Sawyer, Borduin, & Dopp, 2015) and targeted interventions to be more effective when delivered individually than to a group (Smedler, Hjern, Wiklund, Anttila, & Pettersson, 2015; Wilson & Lipsey, 2007). The person delivering the intervention has also been found to moderate intervention effectiveness. For example, interventions delivered by a member of the research team were more effective than those delivered by mental health professionals in Sawyer et al.'s (2015) meta-analysis, and interventions delivered by intervention specialists were more effective than those delivered by teachers in Park-Higgerson, Perumean-Chaney, Bartolucci, Grimley, and Singh (2008)'s quantitative review. School-based interventions have been found to be more effective in high school than in middle school (Hahn et al., 2007) and to be associated with the amount of training the teachers received (Ttofi & Farrington, 2011). The size of the effect of interventions to reduce aggressive behaviours has also been found to vary depending on how the outcome is assessed. For example, both Grove, Evans, Pastor, and Mack's (2008) and Sawyer et al.'s (2015) meta-analyses found that the reduction in aggressive behaviour was more pronounced when the outcome was measured via official records. In the former, that effect was significantly larger than the effect found for self-reports, and in the latter, it was significantly larger than the effect when the outcome was assessed via parent reports. Finally, Ttofi and Farrington (2011) found that anti-bullying school-based interventions evaluated before 2003 were more effective than those evaluated more recently, and interventions implemented in Norway were more effective than those implemented elsewhere. These findings suggest that children from different cultures may vary in the extent to which they engage with interventions to reduce aggressive behaviour and that they may have become less receptive of such interventions over time. In terms of informing our study, these findings indicate that it is important to test whether date of publication and geographical location also moderate the effectiveness of interventions.
Previous studies of the effectiveness of interventions for aggression have used traditional meta-analysis, which is limited by the assumption of independence of effect sizes that prevents more than one effect size from being included from each study. The present study applies a multi-level meta-analysis, which relaxes that assumption. Multi-level meta-analysis allows all effect sizes from studies that report multiple comparisons to be included as the modelling accounts for the dependence of effect sizes nested within studies (Assink & Wibbelink, 2016). Thus, information is maximized and analysis power improved.
In the present study, we aim to identify what works for whom in the reduction of aggressive behaviour. In order to do this, we classify components of the interventions using the BCT taxonomy and test which BCTs are most effective for universal and for targeted interventions separately. In addition, we examine the moderators of intervention effectiveness highlighted in this introduction with the objective of confirming their moderation effect in interventions with adolescents. The moderators that will be examined include characteristics of the intervention such as duration, characteristics of the participants such as gender and aspects of the study design such as outcome informant.
Section snippets
Method
The systematic review protocol was registered on PROSPERO (http://www.crd.york.ac.uk/PROSPERO/display_record.php?ID=CRD42018088811).
Characteristics of included studies
One hundred and twelve studies met the inclusion criteria of which 95 provided sufficient data to calculate effect sizes allowing inclusion in the analysis. These studies were reported in English between 1979 and 2018. Ninety-one per cent were published (87% in academic journals and 3% in books), while the rest were unpublished (8% were dissertations and one record was an institutional report). All included studies comprised 111,151 young people (53,409 in control groups and 57,742 in
Discussion
The present multilevel meta-analysis assessed whether psychosocial interventions were effective in reducing aggression among adolescents and attempted to identify which characteristics of the study, the intervention and the adolescents moderated intervention effectiveness. Across all psychosocial interventions included in the review, we found a statistically significant small-to-medium overall effect size of 0.28. This corresponds to a 10% decrease in aggressive behaviour in contrast with a
Conclusion
This is the first multilevel meta-analysis on interventions to reduce aggressive behaviour in adolescents and the first to examine the role of individual BCTs. We found that psychosocial interventions are effective in reducing aggression among adolescents, especially when they are targeted to young people at greater risk of being aggressive. We found that shorter interventions were more effective than longer interventions, and interventions delivered by intervention professionals were more
Role of funding sources
Funding for this study was provided indirectly by the Department of Psychology University of Sheffield Cathedral Court 1 Vicar Lane Sheffield S1 2LT United Kingdom, through a Teaching Fellowship awarded to the main author. The sponsor had no role in study design, collection, analysis or interpretation of the data, writing the manuscript, or the decision to submit the paper for publication.
Contributors
LCE designed the study and wrote the protocol. RR, PN and CJA revised the protocol and made amendments to it. LCE conducted literature searches. LCE and MRD screened records for inclusion and assessed risk of bias. LCE and OCD extracted data from included studies. LCE conducted the statistical analysis. LCE wrote the first draft of the manuscript and all authors contributed to and have approved the final manuscript.
Declaration of Competing Interest
All authors declare that they have no conflicts of interest.
Acknowledgements
The authors wish to thank Brechtje de Mooji for her assistance on the statistical analysis and acknowledge the support of NIHR Manchester Biomedical Research Centre and NIHR Greater Manchester Patient Safety Translational Research Centre.
Laura Castillo-Eito is a PhD candidate in the University of Sheffield, UK. She undertook a bachelor's in psychology at the University of Zaragoza, Spain, with mention in Social Psychology. Her final project was on the relationship between social status inside a prison and social reintegration. She did a master on Psychological Interventions in the Social Environment at the University of Valencia, Spain. Her dissertation was the evaluation of an intimate partner violence prevention program
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Laura Castillo-Eito is a PhD candidate in the University of Sheffield, UK. She undertook a bachelor's in psychology at the University of Zaragoza, Spain, with mention in Social Psychology. Her final project was on the relationship between social status inside a prison and social reintegration. She did a master on Psychological Interventions in the Social Environment at the University of Valencia, Spain. Her dissertation was the evaluation of an intimate partner violence prevention program targeted to adolescents in a young offender institution. Her research interests are behaviour change in adolescence, antisocial behaviour and aggression.