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DOI: 10.1542/peds.2014-0832
; originally published online September 8, 2014;Pediatrics
Lucy Bowes, Dieter Wolke, Carol Joinson, Suzet Tanya Lereya and Glyn Lewis
Cohort Study
Sibling Bullying and Risk of Depression, Anxiety, and Self-Harm: A Prospective
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located on the World Wide Web at:
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of Pediatrics. All rights reserved. Print ISSN: 0031-4005. Online ISSN: 1098-4275.
Boulevard, Elk Grove Village, Illinois, 60007. Copyright © 2014 by the American Academy
published, and trademarked by the American Academy of Pediatrics, 141 Northwest Point
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Sibling Bullying and Risk of Depression, Anxiety, and
Self-Harm: A Prospective Cohort Study
WHAT’S KNOWN ON THIS SUBJECT: Recent reviews suggest that
children bullied by siblings are at increased risk of internalizing
symptoms. It is not known whether being bullied by a sibling
increases risk of psychiatric disorders such as depression,
anxiety, and self-harm.
WHAT THIS STUDY ADDS: Using a large, community-based birth
cohort, we found that being bullied by a sibling is prospectively
associated with a doubling in the odds of both depression and
self-harm at 18 years in young adults.
abstract
OBJECTIVES: Being the victim of peer bullying is associated with in-
creased risk of psychopathology, yet it is not known whether similar
experiences of bullying increase risk of psychiatric disorder when the
perpetrator is a sibling. We tested whether being bullied by a sibling is
prospectively associated with depression, anxiety, and self-harm in
early adulthood.
METHODS: We conducted a longitudinal study using data from .6900
participants of a UK community-based birth cohort (Avon Longitudinal
Study of Parents and Children) who reported on sibling bullying at 12
years. Our main outcome measures were depression, anxiety, and
self-harm, assessed using the Clinical Interview Schedule–Revised
during clinic assessments when participants were 18.
RESULTS: Children who were frequently bullied were approximately
twice as likely to have depression (odds ratio [OR] = 2.16; 95% confi-
dence interval [CI], 1.33–3.51; P,.001), self-harm (OR = 2.56; 95% CI,
1.63–4.02; P,.001), and anxiety (OR = 1.83; 95% CI, 1.19–2.81; P,
.001) as children who were not bullied by siblings. The ORs were only
slightly attenuated after adjustment for a range of confounding in-
dividual, family, and peer factors. The population-attributable fractions
suggested that 13.0% (95% CI, 1.0%–24.7%) of depression and 19.3%
(95% CI, 7.6%–29.6%) of self-harm could be explained by being the victim
of sibling bullying if these were causal relationships.
CONCLUSIONS: Being bullied by a sibling is a potential risk factor for
depression and self-harm in early adulthood. Our results suggest that
interventions designed to target sibling bullying should be devised and
evaluated. Pediatrics 2014;134:1–8
AUTHORS: Lucy Bowes, PhD,
a
Dieter Wolke, PhD,
b
Carol
Joinson, PhD,
c
Suzet Tanya Lereya, PhD,
b
and Glyn Lewis,
PhD
d
a
Department of Social Policy and Intervention, University of
Oxford, Oxford, United Kingdom;
b
Department of Psychology and
Division of Mental Health & Wellbeing, University of Warwick,
Coventry, United Kingdom;
c
Centre for Mental Health, Addiction
and Suicide Research, School of Social & Community Medicine,
University of Bristol, Bristol, United Kingdom; and
d
Division of
Psychiatry, Faculty of Brain Sciences, University College London,
London, United Kingdom
KEY WORDS
siblings, bullying, depression, anxiety, self-harm, longitudinal,
ALSPAC
ABBREVIATIONS
ALSPAC—Avon Longitudinal Study of Parents and Children
CI—confidence interval
OR—odds ratio
Dr Bowes and Professor Wolke designed and conceptualized the
study; Dr Bowes performed all data analysis and drafted the
initial manuscript; Dr Joinson, Dr Lereya, and Professor Lewis
critically reviewed the manuscript and helped in redrafting; and
all authors approved the final manuscript as submitted.
www.pediatrics.org/cgi/doi/10.1542/peds.2014-0832
doi:10.1542/peds.2014-0832
Accepted for publication Jun 25, 2014
Address correspondence to Lucy Bowes, PhD, Department of
Social Policy and Intervention, University of Oxford, Barnett
House, 33 Wellington Square, Oxford OX1 2ER, United Kingdom.
E-mail: lucy.bowes@spi.ox.ac.uk
PEDIATRICS (ISSN Numbers: Print, 0031-4005; Online, 1098-4275).
Copyright © 2014 by the American Academy of Pediatrics
FINANCIAL DISCLOSURE: The authors have indicated they have
no financial relationships relevant to this article to disclose.
FUNDING: The United Kingdom Medical Research Council and
the Wellcome Trust and the University of Bristol provide core
support for the Avon Longitudinal Study of Parents and Children.
Dr Bowes was partly supported by a grant of the Jacobs
Foundation. Professor Wolke and Dr Lereya were partly
supported by grant ES/K003593/1 of the Economic and Social
Research Council.
POTENTIAL CONFLICT OF INTEREST: The authors have indicated
they have no potential conflicts of interest to disclose.
PEDIATRICS Volume 134, Number 4, October 2014 1
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Being victimized by bullies has been as-
sociated with an increased risk of de-
pression, anxiety, and self-harm.
1–3
It is
not known whether being the victim of
bullying increases risk of psychiatric
disorder when the perpetrator is a sib-
ling. Sibling bullying is a specifictypeof
aggressive behavior that is repeated
over time, intended both to cause harm
and to dominate.
4
Several studies have
provided evidence of an association be-
tween sibling bullying and increased
internalizing symptoms.
5–12
However,
most have either been retrospective
13
or
cross-sectional in design,
5–7,10,11
so they
do not allow inference of the direction of
effects and are susceptible to recall bias.
There is evidence that high levels of
sibling conflict are associated with an
increased risk of later internalizing
symptoms.
9,14–17
To our knowledge, no
previous studies have examined whether
being the victim of sibling bullying is
prospectively associated with psychiat-
ric diagnoses in young adults. According
to socio-ecological theory,
18,19
sibling
relationships, as with other relation-
ships, vary as a function of family, peer,
and individual factors that may also in-
crease risk of psychiatric disorder.
11,18
Such factors include high levels of
stress,
20–22
family violence,
22,23
peer vic-
timization,
6
and children’s internalizing
and externalizing difficulties.
23
Amulti-
variate approach that adjusts for such
factors is needed. Using data from
.6000 families from a UK birth cohort,
we tested the hypothesis that being the
victim of sibling bullying during child-
hood is independently associated with
an increased risk of depression, anxiety,
and self-harm at 18 years.
METHODS
Data Source
The sample was made up of participants
from the Avon Longitudinal Study of
Parents and Children (ALSPAC). ALSPAC
recruited 14 541 pregnant women resi-
dent in Avon, England with expected
dates of delivery between April 1, 1991
and December 31, 1992. Of the 14 541
initial pregnancies (ie, in which mothers
enrolled and returned $1 question-
naire or attended a “Children in Focus”
clinic), 13 988 children were alive at 12
months of age. Children were invited to
attend 9 assessment clinics, including
face-to-face interviews and psychologi-
cal and physical tests, from age 7 years
onward. The tests administered at each
assessment wave varied. (Details are
available on a fully searchable data
dictionary at http://www.bris.ac.uk/alspac/
researchers/data-access/data-dictionary/.)
Ethical approval for the study was ob-
tained from the ALSPAC Ethics and Law
Committee and the Local Research Eth-
ics Committees. The phases of enroll-
ment are described in more detail in the
cohort profile paper.
24
Sample
At the 12-year assessment, questionnaires
were sent out to 11 132 families. Of these,
7505 (67.4%) were returned completed,
3604 were not returned, and 23 were
returned blank. Our starting sample
consisted of 6928 children who answered
detailed questions on sibling bullying
through a postal questionnaire in 2003
and 2004, completed at mean age 12
years; 477 children did not have a sibling
and so did not answer this questionnaire.
Twi n s ( n= 173) were excluded, given
previous literature suggesting that the
sibling relationship between twins may
be distinct from that of singletons.
25,26
Outcome data were available for 3452
adolescents at 18 years. A sample with
complete data across all exposure, out-
come, and confounding variables (n=
2002) was used to investigate the main
and adjusted association between sibling
bullying and depression at 18. Young
adults who attended the clinic at 18 were
morelikelytohavehigherfamilysocial
class and mothers with higher educa-
tional attainment. Those lost to follow-up
were no more likely to have reported
sibling bullying (odds ratio [OR] = 0.99;
95% confidence interval [CI], 0.96–1.03;
P= .68) than those with data on all vari-
ables. To address the possibility of bias,
we also conducted analyses using im-
puted data sets, allowing participants
with incomplete data to be included in the
analyses. All missing data were imputed,
and all analyses were repeated using the
same sample (N= 5715).
Assessment of Sibling Bullying
Sibling bullying was assessed when
children were 12 years (mean 12.1 years,
age range 11.9–15.1 years, SD 9.5
months) with a standard sibling bullying
questionnaire
6
adapted from the widely
used Olweus Bullying Questionnaire.
27
Children were first asked whether they
had a sibling. Of the children who an-
swered this questionnaire, 7005 (93.3%)
reported that they had a sibling, and 477
(6.4%) reported that they did not. Chil-
dren with siblings were then informed
that they would be asked about bullying
by brothers and sisters and told, “This
means when a brother or sister tries to
upset you by saying nasty and hurtful
things, or completely ignores you from
their group of friends, hits, kicks, pushes
or shoves you around, tells lies or makes
up false rumors about you.”Children
were asked whether they had been bul-
lied by a brother or sister at home in the
last 6 months, responding “never”(N=
3643, 52.6%), “only ever once or twice”
(N= 1191, 17.2%), “2 or 3 times a month”
(N=645,9.3%),“about once a week”(N=
663, 9.6%), and “several times a week”
(N= 786, 11.4%). Children were then
asked to report how often different types
of bullying had occurred (Table 1), using
the same frequency measures (internal
consistency a= .78). Children were also
asked to report how old they were when
this first happened (mean age 8.3 years).
Outcomes
Participants completed a self-administered
computerized version of the Clinical
Interview Schedule–Revised (CIS-R)
28
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at the 18-year research clinic (mean
age 17 years, 10 months) conducted in
2009 to 2010. The Clinical Interview
Schedule–Revised is designed for, and
has been widely used in, community
samples
29
and has an estimated test–
retest reliability of 0.74.
28
Depression
We assessed depression by using a bina-
ry variable (depressed, not depressed);
cases were those meeting criteria for
mild, moderate, or severe depression as
listed in the International Classification
of Diseases, 10th Revision.
Anxiety
A binary variable (anxiety present, not
present) was used, with cases defined
as those with the presence of any of the
following 5 anxiety disorders: general-
ized anxiety disorder, social phobia,
specific (isolated) phobia, panic disor-
der, or agoraphobia, according to In-
ternational Classification of Diseases,
10th Revision criteria.
Self-Harm
We assessed self-harm in the previous
year by using a binary variable (self-harm,
no self-harm) coded from responses to
the following questions: “Have you ever
hurt yourself on purpose in any way (eg,
by taking an overdose of pills, or by cut-
ting yourself)?”If yes, “How many times
have you harmed yourself in the last
year?”(not in the past year [coded 0]
versus once, 2–5times.6–10 times, or
.10 times [coded 1]).
Potential Confounders
Potential confounders were selected
a priori based on the research litera-
ture for bullying (both sibling and peer)
and family violence. We selected con-
founders that occurred at or before age
8, the mean onset of sibling bullying. In
addition, we also included the earliest
available self-reported measure of de-
pressive symptoms (age 10).
Individual Characteristics
We assessed children’s internalizing
and externalizing problems by using
maternal reports from the Strengths
and Difficulties Questionnaire
30
when
children were 7 years old (original in-
ternal consistency across subscales,
a= .73; in the current study, a= .70).
We assessed peer victimization when
children were 8 years of age by using a
modified version of the Bullying and
Friendship Interview Schedule
31
(original
internal consistency, a= .77; in the cur-
rent study, a= .71). We assessed de-
pressive mood by using the self-reported
Short Moods and Feelings Question-
naire,
32
when children were 10 years old
(original internal consistency, a= .86; in
the current study, a=.80).
32
Family Characteristics
The analysis was adjusted for a range of
family factors derived from maternal
reports when children were 8 years of
age. These included child birth order
(first or later born), mother’s marital
status (percentage of mothers married
for first time versus divorced or sepa-
rated), number of children living at
home (#2vs$3), presence of both bi-
ological parents in the family, and sibling
gender, assessed as the percentage of
participants with an older brother, an
older sister, a younger brother, and a
younger sister.
We assessed parental occupational social
class based on the lower of the mother or
partner’s occupational social class
33
and
dichotomized into professional, mana-
gerial, or skilled professions and partly
or unskilled occupations, highest ma-
ternal education (coded as [i] advanced-
level qualifications, university degree, or
ordinary-level qualifications or [ii] cer-
tificate of secondary school education,
vocational, or none). We measured ma-
ternal depression (assessed during
pregnancy, at 18 weeks’gestation) by
using the Edinburgh Postnatal De-
pression Scale
34
(original internal con-
sistency, a= .87; in the current study,
a= .85), obtained using a postal ques-
tionnaire. We assessed child maltreat-
ment (no or present) when the study
child was 7 years old by using maternal
reports of study children’sexposureto
stressful life events between 5 and 7
years of age. The items included in this
questionnaire were taken from other
studies.
35,36
A score of 1 was coded if
parents responded “yes”to any item re-
lating to physical or sexual abuse or
reported that the study child had been
put into care. We assessed domestic
violence by using items from an
adapted life events inventory,
35
and
TABLE 1 Description of Sibling Bullying in Boys and Girls
Frequency of Bullying Total Sample, N(%) Boys, N(%) Girls, N(%)
Sibling bullying, all types
Never 3643 (52.6) 1786 (49.0) 1857 (51.0)
Only ever once or twice 1191 (17.2) 529 (44.4) 662 (55.6)
2 or 3 times a month 645 (9.3) 295 (45.7) 350 (54.3)
About once a week 663 (9.6) 275 (41.5) 388 (58.5)
Several times a week 786 (11.4) 351 (44.7) 435 (55.3)
Of those who reported sibling bullying (N= 3285)
Type of bullying (% several times a week)
Hit, kicked, pushed, or shoved 416 (12.7) 185 (12.8) 231 (12.6)
Possessions damaged or taken 65 (2.0) 32 (2.3) 33 (1.8)
Called names 760 (23.1) 329 (22.7) 431 (23.4)
Made fun of 503 (15.4) 235 (16.3) 268 (14.7)
Ignored or left out of games or
social groups
157 (4.9) 86 (6.0) 71 (3.9)
Told lies or had rumors spread
about them
114 (3.5) 64 (4.4) 50 (2.8)
Bullied in another way 74 (2.5) 35 (2.7) 39 (2.4)
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it was considered present if mothers
reported experiencing physical or emo-
tional cruelty from their partner at any
time during the 4 waves in which these
data were collected (child age 8 months;
1 year, 9 months; 2 years, 9 months; and
3years,11months).
37,38
Statistical Analyses
We used logistic regression analyses to
calculate ORs for depression, anxiety,
and self-harm at 18 years according to
sibling bullying at age 12 (treating the
sibling bullying variable as both an
ordinal scale and as a continuous score
to show dose–response association;
both sets of results shown) in univari-
ate models. We examined whether the
relationship between sibling bullying
and each outcome measure could be
nonlinear by using a quadratic term. We
tested for an interaction between gen-
der and sibling bullying for each of the 3
outcomes. We then introduced con-
founding variables separately into each
model to investigate the impact of pre-
vious mental health problems together
with peer bullying experiences and
family characteristics on the associa-
tions. We used the “punaf”command to
calculate the population attributable
risk and 95% CI from the final multi-
variable logistic regression model. All
analyses were conducted by using Stata
12 (Stata Corp, College Station, TX).
Missing Data
A sample with complete data across all
exposure, outcome, and confounding
variables was used to investigate main
and independent effects of sibling bul-
lying. We also imputed missing data
becausethere is substantial information
on sociodemographic variables that
predict missingness in ALSPAC. Weused a
fully conditional specification as imple-
mented in the Multiple Imputation by
Chained Equations
39
algorithm in Stata
12. The imputation model included
additional variables that either were
associated with missingness or were
predictive of outcomes at 18 years:
maternal age and sociodemographics
in pregnancy and early childhood (full
list available on request). We averaged
parameter estimates over 60 imputed
or completed data sets by using Rubin’s
rules.
40
In longitudinal studies, earlier
measures of child depression can be
used to predict later depression,
41
allowing us to impute up to a starting
sample of 5715 those with $1 measure
of adolescent depression and complete
exposure data.
RESULTS
Children who reported that they expe-
rienced sibling bullying were most
commonly subject to nonphysical bul-
lying suchas being called names(23.1%)
or being made fun of by their sibling
(15.4%) several times a week (Table 1).
There were no differences in type of
bullying experienced by boys and girls.
Table 2 shows individual and family
characteristics of children as a function
of their exposure to sibling bullying.
Children who were bullied by siblings
were more likely to be female and to
have higher levels of emotional and be-
havioral problems at age 7. Children who
were bullied by a sibling reported much
higher rates of peer victimization. In
terms of family characteristics, bullied
children were more likely to have an
older sibling, specifically an older
brother, and were more likely to live in
families with $3 children. More frequent
sibling bullying was associated with
lower social class and with higher levels
of maternal depression during preg-
nancy. Sibling bullying tended to occur in
families with greater levels of domestic
violence and child maltreatment.
Association With Psychiatric
Difficulties at 18 Years
Of the 3452 children who provided data
on both sibling bullying and psychiatric
outcomes at 18 years, 1810 participants
reported that they had not been bullied
by a sibling (50.0% female) (Table 3). Of
these children, 6.4% (N=115)hadde-
pression scores in the clinically signifi-
cant range at 18 years, 9.3% (N=169)
experienced anxiety, and 7.6% (N= 138)
had self-harmed in the previous year. Of
the 786 children who reported that they
had been bullied by a sibling several
times a week (55.3% female), depres-
sion was reported by 12.3% at age 18
years, self-harm occurred in 14.1%, and
anxiety was reported by 16.0%.
Despite a difference in overall preva-
lence, there was no evidence for an in-
teraction between gender and sibling
bullying (P..2) for any of the 3 out-
comes, and analyses were not stratified
by gender.
Children who reported being bullied by
a sibling several times a week had more
than twice the odds of depression and
self-harm at age 18 years compared
with those who were not bullied by their
siblings (Table 3) (depression: OR 2.16;
95% CI, 1.33–3.51; P,.001; self-harm:
OR 2.56; 95% CI, 1.63–4.02). These as-
sociations were only slightly attenu-
ated after adjustment for confounding
factors. We conducted additional sen-
sitivity analyses adjusting for concur-
rent depressive symptoms at 18 years
and found that the association between
sibling bullying and self-harm remained
(adjusted OR = 2.26; 95% CI, 1.40–3.66;
P,.001; additionally adjusted for con-
current depression, OR = 2.02; 95% CI,
1.22–3.35; P,.001). The population-
attributable fractions suggested that
13.0% (95% CI, 1.0%–24.7%) of depression
and 19.3% (95% CI, 7.6%–29.6%) of self-
harm at age 18 could be explained by
being the victim of sibling bullying if
these were causal relationships.
Children who reported being frequently
bullied by a sibling also had higher odds
of anxiety in unadjusted analyses (OR =
1.83; 95% CI, 1.19–2.81; P= .006), but
this association was attenuated after
adjustment for individual and family
4BOWES et al at University of Warwick on September 9, 2014pediatrics.aappublications.orgDownloaded from
characteristics (OR = 1.51; 95% CI,
0.95–2.38; P= .08).
There was no evidence for nonlinear
relationships between sibling bullying
and any of the 3 outcomes (P..3).
Missing Data Analyses
We repeated analyses using the im-
puted data set (Table 3). Associations
between sibling bullying and each
outcome were typically slightly lower
in the imputed analyses (eg, adjusted
OR for depression in unimputed data
set = 1.85; 95% CI, 1.11–3.09; in imputed
data set, OR = 1.64; 95% CI, 1.12–2.42)
but were consistent with the previous
findings based on complete cases.
DISCUSSION
Using data from a large, prospective
cohort study, we found evidence of
strong dose–response associations be-
tween being the victim of sibling bully-
ing at age 12 years and depression and
self-harm at 18 years. The associations
were similar for boys and girls, and they
held true even after we controlled for
a range of confounders. We also found
some evidence of an increase of anxiety
at follow-up, although this association
did not remain after adjustment for
concurrent depression at 18 years.
To our knowledge, our study is the first
longitudinal study to investigate the
prospective association between sib-
ling bullying and the emergence of
clinical outcomes in early adulthood.
Our findings are consistent with those
of a cross-sectional study by Tucker and
colleagues
7
that reported evidence of
an increased risk of symptoms of de-
pression, anxiety, and anger among
adolescents exposed to sibling aggres-
sion. Our findings are also in line with
results of recent meta-analyses sug-
gesting an association between sibling
aggression and internalizing symp-
toms.
1,17
Strengths of our study include
the large sample size and extended follow-
up, our detailed self-report measure of
TABLE 2 Individual and Family Characteristics of Sibling Victims
Sibling Bullying (Last 6 mo) P
Never (N= 3643),
% or M (SD)
Only Ever Once or Twice
(N= 1191), % or M (SD)
2 or 3 Times a Month
(N= 645), % or M (SD)
About Once a Week
(N= 663), % or M (SD)
Several Times a Week
(N= 786), % or M (SD)
Individual characteristics
Male 49.0 44.4 45.7 41.2 44.7 ,.001
Child’s age when first bullied by sibling, —8.92 (2.34) 8.38 (2.26) 8.21 (2.37) 7.59 (2.65) ,.001
Early internalizing problems 1.44 (1.61) 1.51 (1.71) 1.47 (1.68) 1.68 (1.69) 1.74 (1.77) ,.001
Early externalizing problems 1.41 (1.39) 1.58 (1.40) 1.61 (1.45) 1.71 (1.48) 1.96 (1.59) ,.001
Frequently bullied by peers 16.8 20.8 21.3 20.9 26.3 ,.001
Family characteristics
First-born child 49.5 37.5 34.3 39.0 34.0 ,.001
Divorced or separated 10.5 10.0 11.3 9.6 12.1
No. of children living at home (% $3) 42.3 49.4 51.2 51.9 56.7 ,.001
Child has older brother (%) 34.4 45.7 49.4 51.3 54.9 ,.001
Child has older sister (%) 39.4 46.0 43.4 42.6 40.6 .14
Lower parental social class 45.9 45.5 43.8 45.5 54.2 .05
Maternal education (ordinary-levels or less) 57.0 55.1 53.7 52.9 60.6 .69
Maternal depression 6.26 (4.53) 6.34 (4.40) 6.57 (4.49) 7.01 (4.76) 7.05 (4.76) ,.001
Maltreated by adult 13.0 14.4 14.8 13.9 18.6 .002
Domestic violence 21.0 24.0 23.9 26.7 30.9 ,.001
—, answer not applicable.
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sibling bullying, and our ability to adjust
for a large number of potential con-
founders.
A potential limitation of the study is that
our measure of sibling bullying was
self-reported. People who are prone to
depression may be more likely to per-
ceive or report bullying. To address this
limitation, we adjusted for emotional
and behavioral problems reported by
mothers at 7 years of age, before the
self-reported mean onset of sibling
bullying occurred, and self-reported
depressive symptoms at age 10. This
approach could have led to over-
adjustment because siblingbullying was
reported on average starting at age 8,
before our Short Moods and Feelings
Questionnaire measure. Finally, in sen-
sitivityanalyses we additionally adjusted
for concurrent depression at 18 years
when examining associations between
sibling bullying, self-harm, and anxiety.
A second limitation is the loss to follow-
up from the original ALSPAC sample.
Those who completed the CIS-R did not
differ in their reports of sibling bullying
at age 12 compa red with those who were
lost to follow-up, and the results of our
imputation analyses were consistent
with our complete case findings. We
therefore think it is unlikely that our
findings could be explained by attrition.
A third potential limitation is that al-
though we adjusted for a number of
potential confounders, we cannot exclude
the possibility of residual confounding.
For example, there is evidence that ge-
netic influences increase children’srisk
of peer victimization,
42,43
but the impact
of peer victimization on children’sinter-
nalizing symptoms has been shown to be
environmentally mediated.
44
It is not
known whether this is also the case for
sibling victimization. Lastly, participants
retrospectively reported the age at
which sibling victimization began. We
adjusted for confounders occurring
before the mean onset of sibling vic-
timization, but this may have led to
TABLE 3 Prevalence and ORs for Depression, Self-Harm, and Anxiety at Age 18 According to Self-Reports of Sibling Bullying at Age 12
Outcome Frequency of Sibling Bullying Linear Trend
Never (N= 3643) Only Ever Once or Twice
(N= 1191)
2 or 3 Times a Month
(N=645)
About Once a Week
(N= 663)
Several Times a Week
(N=786)
Depression
% yes 6.4 6.8 9.1 6.8 12.3 —
Unadjusted OR (95% CI) 1.00 0.91 (0.53–1.56) 1.47 (0.83–2.60) 1.25 (0.70–2.24) 2.16 (1.33–3.51)* 1.18 (1.06–1.33)*
Adjusted OR (95% CI) 1.00 0.79 (0.45–1.36) 1.40 (0.78–2.55) 1.00 (0.55–1.81) 1.85 (1.11–3.09)* 1.13 (1.01–1.27)*
Imputed adjusted OR (95% CI) 1.00 0.99 (0.68–1.45) 1.31 (0.86–2.02) 1.10 (0.72–1.69) 1.64 (1.12–2.42)* 1.18 (1.09–1.28)*
Self-harm
% yes 7.6 9.4 8.8 10.7 14.1 —
Unadjusted OR (95% CI) 1.00 1.57 (1.02–2.44)* 1.46 (0.84–2.55) 1.86 (1.13–3.05)* 2.56 (1.63–4.02)* 1.24 (1.12–1.38)*
Adjusted OR (95% CI) 1.00 1.31 (0.84–2.06) 1.40 (0.79–2.47) 1.68 (1.02–2.77)* 2.26 (1.40–3.66)* 1.21 (1.09–1.35)*
Imputed adjusted OR (95% CI) 1.00 1.23 (0.96–1.59) 1.39 (1.01–1.90)* 1.53 (1.15–2.04)* 2.18 (1.41–3.10)* 1.20 (1.08–1.30)*
Anxiety
% yes 9.3 9.9 6.9 10.4 16.0 —
Unadjusted OR (95% CI) 1.00 1.22 (0.81–1.83) 0.57 (0.29–1.11) 0.95 (0.56–1.61) 1.83 (1.19–2.81)* 1.09 (0.98–1.20)
Adjusted OR (95% CI) 1.00 1.08 (0.71–1.63) 0.54 (0.27–1.06) 0.84 (0.49–1.44) 1.55 (0.95–2.38) 1.04 (0.93–1.15)
Imputed adjusted OR (95% CI) 1.00 0.98 (0.71–1.34) 0.82 (0.53–1.26) 1.10 (0.76–1.58) 1.43 (1.03–1.99)* 1.07 (0.99–1.15)
Unadjusted and adjusted analyses used complete cases (N= 3452).
Adjusted model includes the following covariates: individual characteristics: gender, mother-reported emotional and conduct problems at age 7, peer victimization at age 8, self-repor ted depression at age 10; family characteristics: first-born versus not,
number of children in family, mother’s marital status, parental social class, maternal education, mother’s history of depression, domestic violence and maltreatment.
*P,.05.
6BOWES et al at University of Warwick on September 9, 2014pediatrics.aappublications.orgDownloaded from
overadjustment if sibling victimization
occurred before age 8.
Implications and Conclusions
Victims of sibling bullying are twice as
likely to develop depression by early
adulthood and to report self-harming
within the previous year when com-
pared with children not bullied by sib-
lings. There is a growing concern about
bullying occurring at school, at work, or
by adult partners. In contrast, sibling
bullying is neglected by researchers,
clinicians, and policymakers. Although
sibling bullying tends to occur more
often in families characterized by high
levels of conflict and violence,
45
our
findings suggest that sibling bullying
is independently associated with the
emergence of depression and self-
harm once such family risk factors
have been taken into account.
Unlike peer groups, sibling relation-
ships endure throughout development,
with little opportunity for victims to
escape. Our results suggest that being
bullied by siblings may not be a harm-
less experience in children’s lives but
a risk factor for enduring mental
health problems. Because sibling bul-
lying often occurs alongside interpar-
ental conflict and in families with poor
parent–child relationships, it may be
important to integrate siblings into
child and family programs. However,
given that we observe an association
over and above the effects of multiple
family risk factors, our findings argue
for the development of interventions
specifically designed to target sibling
bullying. Existing programs that tar-
get the sibling relationship more
broadly
46,47
should be systematically
evaluated to determine whether they
lead to a reduction in sibling bullying
and psychological harm.
ACKNOWLEDGMENTS
We are extremely grateful to all the
families who took part in this study,
the midwives for help in recruiting
them, and the whole ALSPAC team,
which includes interviewers, computer
and laboratory technicians, clerical
workers, research scientists, volunteers,
managers, receptionists, and nurses.
The ALSPAC data resource is publicly
available; see http://www.bristol.ac.uk/
alspac/researchers/data-access/ for
further details.
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DOI: 10.1542/peds.2014-0832
; originally published online September 8, 2014;Pediatrics
Lucy Bowes, Dieter Wolke, Carol Joinson, Suzet Tanya Lereya and Glyn Lewis
Cohort Study
Sibling Bullying and Risk of Depression, Anxiety, and Self-Harm: A Prospective
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