Bullying is becoming an ever more pressing issue for schools, daycare centers, politicians and the public. Everyone agrees that bullying is a serious problem and initiatives are urgently called for to stamp it out. This Campbell Systematic Review studied the effects of anti-bullying programs in schools. The conclusion is that programs generally work and bullying is reduced on average by around 20%. A total of 89 reports were of sufficient quality to be included in the systematic review. The 89 reports describe 53 different studies. However, nine studies did not provide enough data to allow the calculation of an effect size and were, therefore, not included in the final meta-analysis. The overall analysis is therefore based on a total of 44 studies. The 44 different studies were carried out between 1983 and mid-2009 and came from 16 different countries. The included studies were either randomized controlled trials, quasi-randomized trials, age-cohort studies or other controlled studies. Furthermore, the systematic review clearly states that future evaluations should measure the children's situation before and after an anti-bullying program. This should apply to the experimental group as well as the control group to get the most accurate results possible. Executive Summary/Abstract BACKGROUND School bullying has serious short-term and long-term effects on children's physical and mental health. Various anti-bullying programs have been implemented world wide and, more rarely, evaluated. Previous narrative reviews, summarizing the work done on bullying prevention, as well as previous meta-analyses of anti-bullying programs, are limited. The definition of school bullying includes several key elements: physical, verbal, or psychological attack or intimidation that is intended to cause fear, distress, or harm to the victim; an imbalance of power (psychological or physical), with a more powerful child (or children) oppressing less powerful ones; and repeated incidents between the same children over a prolonged period. School bullying can occur in school or on the way to or from school. It is not bullying when two persons of the same strength (physical, psychological, or verbal) victimize each other. OBJECTIVES This report presents a systematic review and meta-analysis of the effectiveness of programs designed to reduce school bullying perpetration and victimization (i.e. being bullied). The authors indicate the pitfalls of previous reviews and explain in detail how the present systematic review and meta-analysis addresses the gaps in the existing literature on bullying prevention. SEARCH STRATEGY In the present report, we go beyond previous reviews by: doing much more extensive searches for evaluations such as hand-searching all volumes of 35 journals from 1983 up to the end of May 2009; searching for international evaluations in 18 electronic databases and in languages other than English; and focusing only on programs that are specifically designed to reduce bullying and not aggressive behavior (i.e. the outcome variables specifically measure bullying). Leading researchers in the area of school bullying were also contacted via e-mail. SELECTION CRITERIA Studies were included in this review if they evaluated the effects of an anti-bullying program by comparing an experimental group who received the intervention with a control group who did not. The word ‘experimental’ here refers to students who received the program and does not necessarily imply randomization. Four types of research design were included: a) randomized experiments, b) experimental-control comparisons with before and after measures of bullying, c) other experimental-control comparisons and d) quasi-experimental age-cohort designs, where students of age X after the intervention were compared with students of the same age X in the same school before the intervention. Both published and unpublished (e.g. PhD theses) reports were included. Reports concerning an evaluation of a program had to clearly indicate that bullying or victimization were included as outcome measures. Bullying and victimization could be measured using self-report questionnaires, peer ratings, teacher ratings, or observational data. RESULTS We found a total of 622 reports that were concerned with bullying prevention. The number of reports on anti-bullying programs and on the necessity of tackling bullying has increased considerably over time. Only 89 of these reports (describing 53 different program evaluations) could be included in our review. Of the 53 different program evaluations, only 44 provided data that permitted the calculation of an effect size for bullying or victimization. Our meta-analysis of these 44 evaluations showed that, overall, school-based anti-bullying programs are effective in reducing bullying and victimization (being bullied). On average, bullying decreased by 20% – 23% and victimization decreased by 17% – 20%. The effects were generally highest in the age-cohort designs and lowest in the randomized experiments. It was not clear, however, that the randomized experiments were methodologically superior in all cases, because sometimes a very small number of schools (between three and seven) were randomly assigned to conditions, and because of other methodological problems such as differential attrition. Various program elements and intervention components were associated with a decrease in both bullying and victimization. Work with peers was associated with an increase in victimization. We received feedback from researchers about our coding of 40 out of 44 programs. Analyses of publication bias show that the observed effect sizes (for both bullying and victimization) were based on an unbiased set of studies. AUTHORS’ CONCLUSIONS Results obtained so far in evaluations of anti-bullying programs are encouraging. The time is ripe to mount a new long-term research strategy on the effectiveness of these programs, based on our findings. The main policy implication of our review is that new anti-bullying programs should be designed and tested based on the key program elements and evaluation components that we have found to be most effective. We recommend that a system of accrediting anti-bullying programs should be developed, supervised by an international body such as the International Observatory on Violence in Schools.
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