School bullying as a risk factor for violence, depression and other adverse outcomes later in life: Implications for protecting school youth.

David P. Farrington and Maria M. TtofiCampbell Collaboration Colloquium, Copenhagen, May 31, 2012

Pernille Due et al.(Denmark)• Due et al. (2005) carried out perhaps the largest study of

the prevalence of being bullied (sometimes or more often during this school term) among nationally representative samples of 11–15 year olds in 28 western industrialised countries (surveying over 4,000 students per country on average). (later extended to 66 countries!)

• Overall, 18 per cent of boys and 15 per cent of girls were bullied according to this fairly demanding criterion.

• In the United States 16 per cent of boys and 11 per cent of girls were bullied.

• In Denmark, 26 per cent of boys and 24 per cent of girls were bullied!

Indications from previous research…

Short term effects:>depressive symptomatology (Bosworth et al,

1999; Van der Wal et al, 2003) =>increased risk for suicidal ideation and self-

injurious behaviour (Kaltiala-Heino et al, 1999) =>eating disorders (Kaltiala-Heino et al, 2000)• Long-term effects: =>later offending (Farrington, 1993; Sourander

et al, 2006; Losel, 2008) => difficulties in trust/intimacy in opposite-sex

and friendly relationships in adulthood (Gilmartin, 1987; Dietz, 1994)

School bullying: Is it really related to later adverse outcomes?

Aims of the review:1. To conduct a systematic review (minimizing bias)2. Meta-analyze data; calculate standardized effect sizes

with the final aim of:a) Establishing whether there is indeed an association

between bullying perpetration/victimization and health/criminal outcomes

b) Establishing where the strongest effect lies; guiding future bullying prevention initiatives (e.g. do victims suffer from low self-esteem?; current findings on empathy: D. Jolliffe)

c) Establishing the unique contribution of school bullying/victimization (i.e. after controlling for covariates) across-time (predictive efficacy)

d) Relating bullying to general criminology (e.g.: bullying prevention = crime prevention?)

Why does bullying/victimization predict health/criminal outcomes? •Persistence of underlying tendency?•Or does occurrence of B/V increase probability

of later outcomes?•E.g. if B is reinforced or B leads to decrease in

bonding to society or increase in antisocial peers

•Can’t distinguish persistent heterogeneity from state dependence in systematic review

•Can test if B/V to H/C is driven by risk factor e.g. impulsiveness or low socioeconomic status

Specified Risk Factors (based on Murray et al. JEC paper on Methodological Quality)

Outcome Measures for British Academy Project

Results of Searches up to March 2012

Have obtained 600 reports screened studies in the systematic review

Of the 436 included reports

Bullying Perpetration versus Violence Later in Life [based only on prospective longitudinal studies]

51 reports on violence from 28 longitudinal studies

Measure of Effect Size (Odds Ratio)• Non-Violent Violent•Non-Bully 225 75

300 •Bully 50 50

100

•OR = (225*50)/(75*50) = 3.0

•OR > 1 indicates desirable effect

Bullying Perpetration vs Violence:Unadjusted OR = 2.97 (95% CI: 2.25 – 3.92) Adj. OR = 2.04 (95% CI: 1.69 – 2.45)

The meaning of OR = 2.04This value of the OR indicates a very strong relationship between bullying perpetration and later violence. For example, if a quarter of children were bullies and a quarter were violent, this value of the OR would correspond to 35.8% of bullies becoming violent, compared with 21.4% of non-bullies. Thus, being a bully would increase the risk of being violent (even after controlling for other childhood risk factors) by about two-thirds.

School Bullying versus Violence: Meta-regressions

Moderator Variables for Heterogeneity (Q = 75.80, p = .0001)

•Age at Time 1/Bullying (range: 8.00 – 15.54 years; M = 12.04; SD =

2.35)•Age at Time 2/Outcome (range: 10.00 – 24.64 years; M = 17.65; SD =

4.83) •Length of the follow-up period (range: 0.42 – 16.50 years; M = 5.61; SD =

4.88) •Number of Covariates (range: 2 – 20; M = 6.93; SD = 5.25)

Meta-Regression Results•Age Time 1: (B= - 0.065; SE = 0.021; p = 0.002) •Length of Follow-Up: (B= - 0.017; SE = 0.009; p = 0.051) •Age Time 2: (B= - 0.033; SE = 0.009; p = 0.0005) •Number of Covariates(B= - 0.013; SE = 0.010; p = 0.185) Caveat: many uncontrolled variablesNo publication bias

Some further findings…Bullying Perpetration versus Offending

48 reports on offending from 29 longitudinal studies

Bullying Perpetration vs Offending:Unadjusted OR = 2.54 (95% CI: 2.05 – 3.14) Adjusted OR = 1.89 (95% CI: 1.60 – 2.23)

The meaning of OR = 1.89

This OR indicates quite a strong relationship between bullying perpetration and later offending. For example, if a quarter of children were bullies and a quarter were offenders, this value of the OR would correspond to 34.5% of bullies becoming offenders, compared with 21.8% of non-bullies. Thus, being a bully would increase the risk of being an offender (even after controlling for other childhood risk factors) by more than half.

School Bullying versus Offending: Meta-regressions

Moderator Variables for Heterogeneity (Q = 36.82, p = .001)

•Age at Time 1/Bullying (range: 6.23 – 15.54 years; M = 11.26; SD =

2.68)•Age at Time 2/Outcome (range: 10.00 – 24.64 years; M = 17.10; SD =

4.91)•Length of the follow-up period (range: 0.42 – 16.50 years; M = 5.84; SD =

4.56)•Number of Covariates (range: 1 – 20; M = 7.00; SD = 5.22)

Meta-Regression Results•Age Time 1: (B = .019, SE = .024, p = .428) •Length of Follow-Up: (B = -.027, SE = .012, p = .018) •Age Time 2: (B = -.025, SE = .012, p = .039) •Number of Covariates(B = -.027, SE = .013, p = .037)

Some further findings…Bullying Perpetration versus Drug Use

23 reports on drug use from 13 longitudinal studies

Bullying Perpetration vs. Drug Use:Unadjusted OR = 2.44 (95% CI: 1.73 – 3.43) Adjusted OR = 1.49 (95% CI: 1.21 – 1.84)

The meaning of OR = 1.49•This value of the OR indicates a moderate

relationship between bullying perpetration and later drug use. For example, if a quarter of children were bullies and a quarter were drug users, this value of the OR would correspond to 30.9% of bullies doing drugs, compared with 23.0% of non-bullies. Thus, being a bully would increase the risk of drug use later in life (even after controlling for other childhood risk factors) by about one-third.

Some further findings…Bullying Victimization versus Depression

75 reports on depression from 49 longitudinal studies

Bullying Victimization vs. Depression:Unadjusted OR = 1.99 (95% CI: 1.69 – 2.33) Adjusted OR = 1.71 (95% CI: 1.49 – 1.96)

The meaning of OR = 1.71

•This value of OR indicates a strong relationship between bullying victimization and depression. For example, if a quarter of children were victims and a quarter were depressed, this value of the OR would correspond to 33.0% of victims becoming depressed, compared with 22.3% of non-victims. Thus, being a victim would increase the risk of being depressed (even after controlling for other childhood risk factors) by about half.

Bullying victimization versus Depression: Meta-regressions

Moderator Variables for Heterogeneity (Q = 50.88, p = .0001) •Age at Time 1/Bullying (range: 8.00 – 18.00 years; M = 12.32; SD =

2.74)•Age at Time 2/Outcome (range: 10.00 – 47.00 years; M = 19.45; SD =

9.64)•Length of the follow-up period (range: 1.00 – 36.00 years; M = 7.13; SD =

8.79)•Number of Covariates (range: 1 – 20; M =6.42; SD = 5.06)

Meta-Regression Results•Age Time 1: (B = -.028, SE = .012, p = .026) •Length of Follow-Up: (B = -.007, SE = .004, p = .055) •Age Time 2: (B = -.007, SE = .003, p = .026) •Number of Covariates(B = .020, SE = .008, p = .017)

Other results (adjusted ORs)

•Victimization versus violence: OR = 1.42•(bullying: OR = 2.04)•Victimization versus offending: OR = 1.14•(bullying: OR = 1.89)•Victimization versus drug use: OR = 1.00•(bullying: OR = 1.49)•Bullying versus depression: OR = 1.41•(victimization: OR = 1.71)

Key references• Farrington, D. P., Lösel, F., Ttofi, M. M. and Theodorakis, N. (2012)

School Bullying, Depression and Offending Behaviour Later in Life: An Updated Systematic Review of Longitudinal Studies. Stockholm: Swedish National Council for Crime Prevention.

• Ttofi, M. M., Farrington, D. P. and Lösel, F. (2012) School bullying as a predictor of violence later in life: A systematic review and meta-analysis of prospective longitudinal studies. Aggression and Violent Behaviour.

• Ttofi, M. M., Farrington, D. P., Lösel, F. and Loeber, R. (2011) Do the victims of school bullies tend to become depressed later in life? A systematic review and meta-analysis of longitudinal studies. Journal of Aggression, Conflict and Peace Research, 3, 63-73.  

•  Ttofi, M. M., Farrington, D. P., Lösel, F. and Loeber, R. (2011) The predictive efficiency of school bullying versus later offending: A systematic/meta-analytic review of longitudinal studies. Criminal Behaviour and Mental Health, 21, 80-89.

Conclusions• Bullying is a strong predictor of later offending and

violence, but a weaker predictor of later drug use• Victimization is a strong predictor of later

depression• After controlling for earlier risk factors, so can’t be

explained by these Key Questions:• Does bullying perpetration cause an increase in the

probability of later offending and violence?• Or is bullying perpetration a ‘stepping stone’ on a

developmental sequence leading to offending and violence?

• Equivalent questions for victimization vs depression …

Policy Implications• Programmes that reduce bullying perpetration are

likely to be followed by a reduction in crime and violence

• Programmes that reduce bullying victimization are likely to be followed by a reduction in depression

• Bullying prevention might be regarded as a method of prevention of crime and internalizing problems and a method of promoting health

• Our review indicates the urgent need to implement high quality anti-bullying programmes (see earlier review)

• Need to investigate protective factors that interrupt the continuity from school bullying to later adverse outcomes => a new special issue coming out on this!!!

Research Support:For our review on health/criminal outcomes of school bullying we are again most grateful to:

Swedish National Council for Crime Prevention

www.bra.se

For more information:

Maria M. Ttofi: mt394@cam.ac.uk David P. Farrington: dpf1@cam.ac.ukFriedrich Losel: fal23@cam.ac.uk