BMJ 2015;350:h2694 doi: 10.1136/bmj.h2694
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Editorials
EDITORIALS
Adolescent bullying linked to depression in early
adulthood
Evidence supports early intervention that involves parents, teachers, and young people
Maria M Ttofi lecturer in psychological criminology
Institute of Criminology, University of Cambridge, Cambridge CB3 9DA, UK
Throughout the school years, probably the one thing beyond
schoolwork that young people have in common is the need to
fit in with their peer group. When young people do not fit in,
things may turn ugly.1 We have all heard stories of young people
being the target of racist, homophobic, or other forms of
bullying. Bullying can hamper the psychosocial development
of young people.2 Notably, scientific interest in the topic
emerged after the well publicised suicides of three Norwegian
students in 1982, resulting in a nationwide campaign against
bullying and victimisation.3
In a linked paper (doi:10.1136/bmj.h2469) Bowes and
colleagues4 investigated the long term adverse effect of bullying
by peers on the mental health of victims, with a focus on
depression in early adulthood. The authors used sophisticated
longitudinal analyses from the Avon Longitudinal Study of
Parents and Children (ALSPAC) study, a UK community based
birth cohort, to investigate the predictive efficacy of
victimisation by peers at age 13 years on depression five years
later. The study, based on data from over 2600 adolescents,
showed that those who were frequently victimised had a twofold
increase in odds of later depression compared with their
non-victimised counterparts. Analyses focused on investigating
the unique effect of victimisation on depression over and above
the impact of other contributing factors that may potentially
lead to depression, thus providing as much as possible an
unbiased estimation of effects.5
Bowes and colleagues’ findings are in line with, and also
complement, existing research. Meta-analysis of longitudinal
studies has shown that bullying is a significant risk factor for
depression,6 with bullied teenagers being about twice as likely
as non-bullied ones to feel depressed up to about seven years
later. The current study takes a further step by focusing on
depression meeting diagnostic criteria based on the clinical
interview schedule-revised, an instrument that has been found
to be culturally sensitive in measuring the general latent
construct of anxiety-depression.7 This is important given that
study findings are potentially generalisable to the culturally
diverse UK population.
Participant dropout occurs in all longitudinal studies and, if
systematic, may lead to selection biases and erroneous
conclusions in studies.8 Bowes and colleagues conducted
detailed sensitivity and missing data analyses based on
participants with complete information on all variables, but also
used imputed data, thus investigating thoroughly the possibility
of selection bias. Results were reassuring. The study also
followed a reasonable analytical approach in investigating
whether levels of frequency of victimisation were related to
more adverse effects, and a dose-response relation was
established. Future analyses based on levels of severity of
victimisation may shed further light on the link between
victimisation and depression. Future analyses should also
endorse more dynamic experiences of victimisation as young
people may enter and escape victim roles throughout their school
years.9 Severity of depression may also vary for groups
experiencing persistent versus occasional victimisation. Bowes
and colleagues identified over 250 new victims at age 13 years
who had not reported victimisation at earlier ages, but their
analyses do not investigate stability of victimisation over time.
Such substantial work should lead to further reflection about
the need for early intervention. Effective antibullying
programmes can be seen as a form of public health promotion.6
Advocates of a more sceptical approach may challenge this view
on the grounds that causal effects cannot be established. Bowes
and colleagues acknowledge that causation cannot be claimed
with any certainty. Admittedly, in risk factors research, events
such as maternal depression or peer victimisation cannot be
randomly assigned, and observational studies are the norm10
owing to ethical or other practical considerations. However, this
does not eliminate the possibility of drawing some conclusions
about causality from risk factors research.11
Future analyses of the ALSPAC data need to investigate change
over time within individuals to show whether changes in
depression follow changes in peer victimisation. Although
analyses between individuals (that is, comparisons of different
participants) are the norm in social science, causal conclusions
may be more compelling when based on analyses of change
within individuals, because the concept of cause involves the
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BMJ 2015;350:h2694 doi: 10.1136/bmj.h2694
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EDITORIALS
concept of change within individual units; in other words, with
people essentially acting as their own controls.11 Other
methodological approaches, such as propensity score matching,
may also lead to safer causal inferences.5
Regardless of the above methodological debate, peer
victimisation significantly predicts depression, and societies
need to take measures to protect vulnerable young people. Given
the cross national consistency in the relation between bullying
behaviours and psychosocial adjustment,2 6 Bowes and
colleagues’ work offers clear antibullying messages that should
be endorsed by parents, school authorities, and practitioners
internationally.
Interestingly, Bowes and colleagues establish a clear link
between victimisation and non-reporting to teachers or family
members. Parents and teachers need to be aware of this and
proactively ask children about school experiences beyond
academic matters. Collaborative work between parents, teachers,
and other school staff should also be promoted as it has been
linked to reductions in prevalence of both bullying and
victimisation across antibullying programmes.12 Young people
themselves need to endorse antibullying attitudes, inform adults
about experiences of victimisation, and learn the importance of
not internalising the victim identity.13
Bowes and colleagues’ work will further inform the debate
about peer victimisation and mental health. Future research
should aim to establish the causal mechanisms that link peer
victimisation to depression, thus enabling programme planners
to move towards theoretically driven intervention strategies.
Competing interests: I have read and understood the BMJ policy on
declaration of interests and declare the following: none.
Provenance and peer review: Commissioned; not externally peer
reviewed.
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Nansel TR, Craig W, Overpeck MD, et al. Cross-national consistency in the relationship
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on depression in early adulthood: a prospective cohort study in the United Kingdom. BMJ
2015;350:h2469.
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Ryoo JH, Wang C, Swearer SM. Examination of the change in latent statuses in bullying
behaviors across time. Sch Psychol Q 2015;30:105-22.
Petrosino A. Estimates of randomized controlled trials across six areas of childhood
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Farrington DP. Studying changes within individuals: the causes of offending. In: Rutter
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Ttofi MM. Farrington DP. Effectiveness of school-based programs to reduce bullying: a
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Sharkey JD, Ruderman MA, Mayworm AM, et al. Psychosocial functioning of bullied youth
who adopt versus deny the bully-victim label. Sch Psychol Q 2015;30:91-104.
Cite this as: BMJ 2015;350:h2694
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