Content uploaded by Inga Tidefors
Author content
All content in this area was uploaded by Inga Tidefors
Content may be subject to copyright.
PLEASE SCROLL DOWN FOR ARTICLE
This article was downloaded by:
[Goteborgs Universitetsbibliote]
On:
27 May 2010
Access details:
Access Details: [subscription number 906695022]
Publisher
Routledge
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-
41 Mortimer Street, London W1T 3JH, UK
Journal of Sexual Aggression
Publication details, including instructions for authors and subscription information:
http://www.informaworld.com/smpp/title~content=t713723837
Sibling incest: A literature review and a clinical study
Inga Tideforsa; Hans Arvidssona; Sara Ingevaldsona; Michael Larssonb
a Department of Psychology, University of Gothenburg, Gothenburg, Sweden b Centre for Treatment of
Child Sexual and Physical Abuse, University Hospital, Linköping, Sweden
First published on: 25 May 2010
To cite this Article Tidefors, Inga , Arvidsson, Hans , Ingevaldson, Sara and Larsson, Michael(2010) 'Sibling incest: A
literature review and a clinical study', Journal of Sexual Aggression,, First published on: 25 May 2010 (iFirst)
To link to this Article: DOI: 10.1080/13552600903511667
URL: http://dx.doi.org/10.1080/13552600903511667
Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf
This article may be used for research, teaching and private study purposes. Any substantial or
systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or
distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation that the contents
will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses
should be independently verified with primary sources. The publisher shall not be liable for any loss,
actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly
or indirectly in connection with or arising out of the use of this material.
Sibling incest: A literature review and a
clinical study
Inga Tidefors,
1
* Hans Arvidsson,
1
Sara Ingevaldson
1
&
Michael Larsson
2
1
Department of Psychology, University of Gothenburg, Gothenburg, Sweden &
2
Centre for
Treatment of Child Sexual and Physical Abuse, University Hospital, Linko
¨ping, Sweden
Abstract Few previous studies have explored the characteristics and dynamics of adolescent sibling
incest. The objectives of this paper were twofold: first, to conduct a literature review that accounts for
earlier research in the area, and secondly, to conduct a clinical study to explore differences regarding
the characteristics of a group of adolescent sibling incest offenders (n 21) compared to a group of
adolescent non-sibling offenders (n24). Comparisons were made regarding variables such as family
dysfunction, the offenders’ prior victimization and offending behaviour. The data were derived from
intake assessment files and semi-structured inter views with 45 adolescents who had sexually offended.
The sibling incest offender group had grown up more often in dysfunctional families. Moreover, the
results indicated that the offending behaviour in the sibling incest group was more severe. The study
gives some empirical support for the possibility that sibling incest can be one sign, among others, of
maltreatment during childhood.
Keywords Clinical study; family dysfunction; incest taboo; literature review; sibling incest
Introduction
This paper consists of two parts. First there is an overview of the literature concerning the
phenomena of incest and the incest taboo. Thereafter, an empirical study concerning sibling
insect is presented. The literature review deals with a broad aspect of the phenomena of the
incest taboo and could be seen as an enlarged introduction to the empirical study.
Review of the literature
In carrying out this review, we were interested in the literature on incest and the incest taboo
in general, but we also had a more specific interest in publications concerning sibling
offenders. There have been few studies in the area of sibling incest compared to studies of the
whole group of adolescents who sexually offend and of fatherdaughter incest. Moreover,
sibling incest has often been studied as a part of interfamilial incest and not as a distinct
variable. A recurrent conclusion about sibling incest is that this topic demands further
*Corresponding author: E-mail: inga.tidefors@psy.gu.se
Journal of Sexual Aggression
2010, 114 iFirst article
ISSN 1355-2600 print/1742-6545 online #2010 National Organisation for the Treatment of Abusers
DOI: 10.1080/13552600903511667
Downloaded By: [Goteborgs Universitetsbibliote] At: 11:13 27 May 2010
attention from researchers (Adler & Schutz, 1995) and clinicians (Haskins, 2003; Phillips-
Green, 2002). Sibling abuse is even more underreported than parentchild abuse by parents,
teachers, mental health professionals and others in the community (Caffaro & Conn-Caffaro,
2005). Hence, it might seem puzzling that so few, and especially few recent studies, have
explored the sibling offender group, although this group seems to represent a notable
proportion of the incest cases and, more specifically, of assaults perpetrated by adolescents
(Miranda & Corcoran, 2000; Worling, 2001).
The phenomena of incest and the incest taboo
The incest taboo is based on a complicated combination of biological and sociological
concerns, and a knowledge of the psychological development of a child and this mixture has,
according to Lloyd (1982), contributed to the confusion that sometimes exists among social
service personnel as well as legal professionals in deciding whether or not a sexual act is
abusive. The existence of a universal incest taboo is questioned by some writers from a
historical perspective (Parker, 1996; Scheidel, 1996). deMause (1991) states that instead the
question should be whether there is a universal incest taboo.
Historical perspective. One example that questions the existence of a universal incest taboo is
the rise in brothersister marriages during the Roman occupation of Egypt (Parker, 1996).
These marriages were partly a way to demonstrate an own and ‘‘pure’’ people and partly an
attempt to minimize fragmentation of agricultural land, as daughters also had a right to inherit
property. The reason for this institutionalized incest was mainly materialistic, and can be
understood from this specific context (Parker, 1996; Scheidel, 1996).
Plato recommended men to have sexual contact with boys, but later in history Plato’s
attitude was replaced by norms formed by the church, and sexuality became associated with
feelings of shame (Kahr, 1991). The church made people try to control their sexuality,
including sexuality directed towards a child, and these wishes were projected onto the child,
who was seen as a seducer of the adult. The child was also viewed as being in collusion with
the devil, and many children were burned at the stake (Kahr, 1991). The view of the child as a
seducer of a parent is also known through Freud’s use of Sophocles’ myth about Oedipus. In
this myth, Oedipus seduces his mother, unaware that she is his mother, and is eventually
severely punished for this act. When Oedipus understands/sees what he has done, he takes the
broach from his dead mother and plunges its spikes into his eyes (Kilborne, 2003). An
interesting remark made by Wasserman and Rosenfeld (1992) is that Freud abandoned the
view that patients’ stories about sexual abuse from a father were memories of things that really
had happened, and instead looked at them as fantasies. This shift had consequences during
the entire 20th century in psychiatrists’ tendencies to interpret incest as only fantasies.
Legal perspective. Religious views were influential in shaping the early legislation concerning
sex crimes. Strong religious undertones can be found, for example, in the 1608 Swedish law
concerning incest. These views persisted, and during the sixteenth and seventeenth centuries
both the perpetrator and the victim of incest were sentenced to death. The death penalty for
the perpetrator remained in Sweden until 1864, and until 1937 both the abusing parent and
the child victim were punished (Inger, 1986).
Legislation can be seen as a form of cultural transmission of what behaviour is allowed
versus forbidden, and most countries punish sibling marriages (Aoki, 2005). Aoki (2005)
discusses whether the resistance to brothersister couples is a result of recognizing the medical
and psychological consequences for the offspring, the threat of punishment or an internalized
incest taboo. Turner (2008) argues that legislation is still influenced by morality rather than
2I. Tidefors et al.
Downloaded By: [Goteborgs Universitetsbibliote] At: 11:13 27 May 2010
realism, given that it is now possible, at least in principle, to avoid such births either through
birth control or abortion.
Incest taboo as an inbreeding avoidance. Two main, differing views exist of the phenomenon of
incest taboo, or inbreeding avoidance. ‘‘Whereas the Freudian school proposes that the desire
for incest is ubiquitous and must be met with taboo and repression, the Darwinian school
holds that inbreeding-avoidance is the outcome of evolved adaptive mechanisms’’ (Walter &
Buyske, 2003, p. 353). This evolutionary hypothesis argues that bonding in early childhood
functions to establish behaviours that are adaptive in the context of a high degree of genetic
relatedness (Erickson, 1999; Walter & Buyske, 2003). For example, children living together in
the same kibbutz from birth up to six years seldom form love relationships, while marriages
are common between children coming together in kibitzes after the age of 12 years. The
conclusion is that early bonding results in incest avoidance (Erickson, 1999).
It has been suggested that women are more averse to marrying someone with whom they
grow up compared to men (Walter & Buyske, 2003). The inhibition effect of early childhood
bonding has been explored by studying reactions to fictional cases of sibling incest, where the
participants’reactions were understood in the light of their childhood experiences (Fessler &
Navarrete, 2004). The main result was that co-socialization is associated with a strong
reaction to incestuous behaviour, and that females showed greater aversion to the fictional
cases than did males. Further, it was found that individuals with siblings compared with
individuals without siblings had a more negative reaction to cases describing incestuous
relations and were more positive of punishing incestuous behaviour (Fessler & Navarrete,
2004).
Modern views of the incest taboo. Diggs (1997) talks about a plural taboo, i.e. a taboo against
specific objects: mother, father, daughter and sister/brother taboo. The mother taboo is an
instinctual incest inhibition and the father taboo a cultural incest prohibition. Diggs (1997)
interprets the results from Parker and Parker (1986) as a confirmation of this hypothesis.
Parker and Parker (1986) find that abusing fathers are less involved in the nurturance and care
of their daughters in the first three years of life compared to fathers taking care of their
newborn daughters. The father’s attendance at the delivery of the child could, according to
Diggs (1997), be seen as a modern ritual to strengthen the cultural father taboo.
Immerman and Mackey (1997) suggest a broad interpretation of the incest taboo
focusing upon its function; namely, to protect the sexual development of the child. Thus, they
are focusing upon human mating behaviour, which could be damaged if a child is exposed to
incestuous sexuality. Finkelhor (1979) states that it seems sounder to base the case against
incest upon the fact that the child is unable to consent to sex with adults by virtue of his/her
very status as a child, i.e. the child lacks the knowledge and experience to make a proper
decision about sexuality. The child does not have the freedom, legal or psychological, to give
or refuse consent in a truly independent manner.
Definition of sibling incest. The definition of sibling incest differs between studies. Some
researchers suggest that sibling incest should be defined as a sexual relation between
individuals who have one or both parents in common (Smith & Israel, 1987). Other
researchers find it more meaningful to use the term ‘‘ psychological incest’’, referring to the
violation of sexual barriers that exist between people who call themselves a family (Perlmutter,
Engel & Sager, 1982). In a study by Worling (1995a), one result is that everyone in a sibling
offender group had younger siblings in their home, compared to eight of 28 in a non-sibling
group. This is not surprising, because the common pattern in sibling incest is that the offender
is the older and the victim is the younger sibling (DiGiorgio-Miller, 1998). There appears to
be the need of a younger sibling ‘‘ to make’’ a sibling offender.
Sibling incest 3
Downloaded By: [Goteborgs Universitetsbibliote] At: 11:13 27 May 2010
In some earlier studies sibling incest was described as being less serious than parentchild
incest, and sometimes even described as sexual experimentation (Adler & Schutz, 1995).
Also, in families where sibling incest exists, the non-abusing members try to minimize or make
sense of the sibling incest in different ways (Bass, Taylor, Knudson-Martin & Huenergardt,
2006).
The taboo against sibling incest is sometimes supposed to be weaker than the parent
child incest taboo (Carlson, Maciol & Schneider, 2006; Diggs, 1997). However, sibling incest
is also associated, for both the siblings, with confusion and feelings of being stigmatized
(Carlson et al., 2006). There are novels describing sexual acts between siblings as positive, but
clinical experience shows that the most common pattern is that the older sibling becomes the
abuser of the younger sibling, often against his or her will (DiGiorgio-Miller, 1998; Nyman &
Svensson, 1995).
Prevalence
According to Mendel (1995), the denial of child sex abuse disappeared during the 1970s, but
only abused girls were studied and discussed. However, in studies concerning incest, father
daughter incest is the norm and there are few studies concerning male victims and/or female
perpetrators (Turner, 2008). In deMause’s (1974) historical overview he comments that we
can learn from Greek and Roman history that there has existed an extensive sexual
molestation of boys.
It is important to stress that the prevalence of sexual assault among adolescents is low,
although a substantial proportion of all sexual offences can be attributed to adolescents.
Despite the fact that the majority of sexual assaults are committed by adult men, a significant
minority of sexual assaults, approximately 20%, are committed by juveniles (Barbaree &
Marshall, 2006). However, adolescents who sexually offend are likely to choose their first
victim from within their family (Miranda & Corcoran, 2000). Worling (2001) found that 69%
of the reported interfamilial sexual offenders had assaulted siblings and the rest had assaulted
cousins, nieces and nephews.
One study, based only on child-to-child sexual abuse, found that 51% of these cases were
sibling incest (Shaw, Lewis, Loeb, Rosado & Rodriguez, 2000). In another study of 203
participants that investigated different kinds of aggression among siblings, it was found that
7% reported some sexual behaviour, ranging from kissing and fondling to attempted
intercourse. Notably, 80% of these respondents reported that the behaviour had been
consensual (Hardy, 2001). However, Barbaree and Langton (2006) state that those who
perceive this kind of experience as positive may have been affected in negative ways that they
do not recognize or understand.
Family characteristics
Most studies concerning family characteristics in the background of adolescents who sexually
offend do not distinguish between different subgroups, whereas some are comparing different
types of offenders. Only a few deal exclusively with sibling cases.
An early study investigating 25 families in which sibling incest had occurred (Smith &
Israel, 1987) showed a common pattern of family dynamics. Both parents were inaccessible.
The fathers were deceased, or had abandoned their families after the birth of the child. The
mothers were non-available because of drug addiction, alcoholism and/or mental illness.
Further, families with non-divorced parents were characterized by parents engaged in
extramarital affairs and exposing the children to a sexual climate, i.e. as a child being
4I. Tidefors et al.
Downloaded By: [Goteborgs Universitetsbibliote] At: 11:13 27 May 2010
exposed to parents’sexuality, and sometimes sexual violence and pornography. Rudd and
Herzberger (1999) also point out that the absence of the father in chaotic families can lead to
girls being abused by their brothers. Finally, one study compared 32 adolescent sibling
offenders and 28 adolescent non-sibling offenders (Worling, 1995a). The sibling offender
group reported significantly more marital discord (between parents), parental rejection,
physical discipline, negative family atmosphere and general dissatisfaction with family
relationships. Salazar, Camp, DiClemente and Wingood (2005) summarized studies about
family factors related to sibling incest; namely, parental rejection, abuse and marital conflicts.
Their conclusion is that family dynamics have a key role in creating the context where sibling
incest could occur. The sibling offender has also grown up in families with many children. In a
study by Cyr, Wright, McDuff and Perron (2002), approximately 60% of the families had
more than three children. On average, Rudd and Herzberger (1999) found that the number of
children in the families in their brother incest sample was 6.2. However, in Adler and Schutz’s
(1995) study, the number of children in the families was between two and seven, with a modal
number of two.
Some studies point to neglect as an underlying dimension of sibling incest and that an
older sibling is using a younger sibling to satisfy emotional needs, rather than a need for sexual
gratification (Haskins, 2003; Schwartz, Cavanaugh, Pimental & Prentky, 2006). Parental
rejection was also found to be more frequent in a sibling incest group than in a non-sibling
group (Worling, 1995a). Other studies show that a substantial proportion of parents of sibling
incest offenders had themselves been victims of sexual and/or physical abuse; this could partly
explain the dysfunction in many of these families (Adler & Schutz, 1995; Cyr et al., 2002),
and that a lack of parental involvement makes it possible to act out without being detected
(DiGiorgio-Miller, 1998). Different kinds of abusive behaviour between siblings can also be
described as a triadic affair, including the parents as reinforcing or seeing the abuse without
hindering the children (Graham-Bermann & Cutler, 1994).
Earlier victimization
The frequencies of punitive behaviours or physical victimization during the childhood of
sibling offenders vary between different studies, with Adler and Schutz (1995) finding the
highest frequency of 92%, O’Brien (1991) finding 61%, Becker et al. (1986) only 13.6% and
Cyr et al. (2002) only 12.4%. Possible explanations of the large variation can be attributed to
the different definitions of what punitive behaviours and physical victimization should
include. In Worling’s (1995a) study it was established that the sibling incest offenders
reported significantly more physical punishment than the non-sibling offenders. A prevalent
clinical assumption is that both adolescent and adult sex offenders have been sexually abused
as children, but such a consistent result is not found in studies (Barbaree & Langton, 2006).
Most studies on earlier sexual victimization do not distinguish between different groups of
adolescents who sexually offend. Barbaree and Langton (2006) summarize these studies
saying that a high proportion of adolescents who sexually offend report a history of
sexual victimization. In Adler’s and Schultz’s (1995) study only one in a group of 12 sibling
offenders reported being sexually abused as a child. However, in Worling’s (1995a) study
significantly more sibling offenders reported a history of childhood sexual abuse than did the
non-sibling offenders. Although the sibling offenders have not always themselves been
victims of sexual abuse, they have often been raised in sexually dysfunctional families
(Smith & Israel, 1987).
Sibling incest 5
Downloaded By: [Goteborgs Universitetsbibliote] At: 11:13 27 May 2010
Offending behaviour
Adolescents who sexually offend have also been described in terms of their offending
behaviour or perpetration characteristics, rather than in terms of earlier experiences. Most
studies of sibling incest have focused either upon the victim or the perpetrator, and few have
focused upon the relationship between the siblings (Bass et al., 2006). Results presenting
different aspects of offending behaviour or perpetration characteristics should be viewed with
caution, as they often rely upon memories of the victims or of the perpetrators of abuses that
took place many years ago.
Victim preference. The most common view about victim preference is that sexual abuse by
adolescents is not motivated primarily by sexual urges and that unavailable parents can
contribute to a higher degree of bonding between siblings, and this comfort-seeking can
become sexualized (Salazar et al., 2005). Therefore, propensities for specific victims may not
be as entrenched and, thus, not as predictive as they are for adults (Worling & Curwen, 2000).
However, Seto, Murphy, Page and Ennis (2003) conclude that the role of paedophilic interest
is necessary to understand the aetiology of sexual offending perpetrated by adolescents.
According to Seto et al. (2003), paedophilic interests emerge in late childhood or early
adolescence. However, the results of another study investigating both incest and non-incest
offenders pointed to the fact that there is nothing like ‘‘pure incest’’, and sexual abuse can be
understood as a part of a larger overacting repertoire of deviant sexual behaviour and not as
specific interests concerning choice of victims (Studer & Aylwin, 2006). In discussions about
preference for a special kind of victim, Miranda and Corcoran (2000) state that adolescents
who sexually offend are likely to choose their first victim from within their family, and another
study showed that 69% of the adolescents who sexually offend had assaulted siblings
(Worling, 2001). Sexual abuse of a sibling of the same sex has been shown to be relatively
frequent in reported cases and in most cases when male victims were chosen, they were
children, but when female victims were chosen they were equally likely to be children, peers or
adults (Worling, 1995b). To summarize, a common pattern is that the adolescents who offend
against peers or adults tend to choose female victims, and the group of adolescents who
sexually offend younger children, including sibling offenders, choose female, male or both
genders as victims (Worling, 2001).
Sexual act. Some studies investigating the type of sexual act committed found that intercourse
was more frequent in sibling offender samples than in non-sibling offender samples (Bevc &
Silverman, 2000; Cyr et al., 2002). However, the most common type of sexual act was
fondling and touching of genitals (Adler & Schutz, 1995; Cyr et al., 2002; Smith & Israel,
1987). Other types of sexual acts included oral intercourse, genital exposure (non-physical
abuse) and digital vaginal penetration. Anal penetration was the least frequent type of sexual
contact (Adler & Schutz, 1995; Pierce & Pierce, 1987; Shaw et al., 2000). Penetration was a
more frequent abusive behaviour in a brothersister incest group (70.8%) compared to a
stepfather incest group (27.3%) and a father incest group (34.8%) (Cyr et al., 2002).
Interviews in combination with questionnaire responses from 41 adults who had been abused
by a sibling revealed that the most common sexual act was vaginal or oral intercourse, and that
these intercourses were perceived as coercive. However, little is known about the types of
sexual behaviours involved with regard to acts of sibling incest (Carlson et al., 2006).
Duration. The mean duration of sibling abuse was found to be 28 months in one study (Cyr
et al., 2002) and 22 months in another study (Adler & Schutz, 1995). In a study comparing
father offenders with brother offenders, Rudd and Herzberger (1999) found a difference in
duration between the father group (14.7 years) and the brother group (7.9 years). The period
of abuse being shorter in brother incest is due probably to the fact that the brothers often are
6I. Tidefors et al.
Downloaded By: [Goteborgs Universitetsbibliote] At: 11:13 27 May 2010
older than their victims and thus, when leaving home, the abuses end. Carlson et al. (2006)
summarize studies that took the duration of sibling incest into account and conclude that
reports of duration are wide-ranging, from two months to nine years.
Empirical study
The specific aim of the empirical study was to compare a group of adolescents who had
sexually abused their siblings with another group of adolescents who had abused non-siblings.
The comparison was made partly using family characteristics data, partly using data
concerning the adolescent’s offending behaviour. The following hypotheses were specified,
based on previous research: the sibling offender group had lived in more dysfunctional
families compared to the non-sibling offender group. The sibling offender group had been
psychologically, physically and sexually victimized to a greater extent than the non-sibling
group.
Furthermore, because previous studies are ambivalent on this matter, the present study
also explored whether the two groups differed on characteristics of offending behaviour, i.e.
type of sexual act and the duration of the offending behaviour.
Method
Participants
The target group comprised 45 adolescent males who had committed sexual offences against
children, adolescents or adults. Nine of the boys were voluntary patients of the Swedish
Psychiatric Clinics for Children and Adolescents. Three of these nine outpatient boys lived at
home, whereas the other six were placed in the care of Social Services. Thirty-six boys were
placed at institutions belonging to The National Board of Institutional Care. Of these 36
boys, 12 were placed there compulsorily and 24 were placed by voluntary agreement. The
data collection took place during 20032007. The empirical data for the present study
consisted of retrospective data derived from intake assessment files restored in the Psychiatric
Clinics for Children and Adolescents or in the institutions, and data from semi-structured
interviews with the participants, undertaken by the first author.
Instrument
The intake assessment files included the following variables used in the present study: age at
the time of data collection, ethnic origin, intellectual difficulties (impaired learning abilities),
behavioural/acting-out diagnosis, victim of bullying, having bullied other children, other types
of antisocial behaviour, number of children in the family, sexual abuse by a family member
(sexual abuse perpetrated by a family member towards the boy or towards other victim/
victims), having been sexually abused by a family member, age at time of first committed
sexual assault, the age difference between the boy and his victim(s), type of sexual act, relation
between the boy and the victim(s), duration of the offending behaviour, i.e. single or repeated
offending, and finally if the boy was younger than 14 years on the first abuse occasion.
From the interviews with the participants the following information was gathered:
whether the boy was a victim of psychological or physical abuse, whether he had experienced
divorce in the family, whether he was living or had lived in a foster-home and whether there
had been parental substance abuse.
Sibling incest 7
Downloaded By: [Goteborgs Universitetsbibliote] At: 11:13 27 May 2010
Procedure
Ethical committees in five different areas in Sweden approved the study design. The boys were
recruited with the help of either the psychologist or the head of the institutions. These
individuals also informed fully first the parents, and thereafter the boys, about the purpose of
the study, that participation was voluntary and that the boys could drop out at any time they
wanted to. An informed consent form was administered and signed, first by the parents and
thereafter by the boys. When both parents and the boy had signed, the psychologist or the
head of the institution contacted the first author to decide on a suitable occasion for
interviews and data acquisition. Eight boys (15%) did not want to take part in this study. Of
these eight boys, four were patients at one Psychiatric Clinic for Children and Adolescents,
two were sentenced to shorter time-limited punishments and were placed at a closed
institution and two of these eight boys were placed voluntarily at institutions. The other boys
showed a high tendency to participate. The low number of refusals might be related to the
boys’situations, i.e. most of them living in institutions or being patients in psychiatric care,
which could create an ethical dilemma. Although the participation was formally voluntary,
perhaps the boys thought that they had to agree to participate.
The participants were assigned to two groups: sibling offender (at least one parent was in
common with the victim) and non-sibling offender (all others). Empirical support has been
found (Worling, 1995a) for grouping family dysfunction variables into one cluster. Worling
(1995a) conducted this by using the variables of physical punishment, feelings of parental
rejection and marital discord. Some variables in the present study were chosen to match these
variables: ‘‘victim of physical abuse’’,‘‘victim of psychological abuse’’ and ‘‘divorce in the
family’’. Other variables grouped into the cluster were chosen on the basis of previous studies
(Adler & Schutz, 1995; Ascherman & Safier, 1990; Becker et al., 1986; Cyr et al., 2002;
Rudd & Herzberger, 1999; Smith & Israel, 1987), and as such were thought to be related to
family dysfunction. These variables were ‘‘sexual abuse by a family member’’ (sexual abuse
perpetrated by a family member towards the boy or towards other victim/victims), ‘‘living or
had ever lived in a foster-home’’ and ‘‘parental substance abuse’’ . Each existing indicator of
family dysfunction was given one point, thus the maximum point in this cluster (family cluster
scale) was six. The internal reliability for this cluster was 0.67 (Cronbach’s coefficient alpha).
Statistical analyses
In comparing the sibling offender group and the non-sibling offender group the following
analyses were used: Student’s t-test was used to analyse differences in ages and the family
cluster scale. Considering the distribution of the numbers of siblings, the MannWhitney
U-test was used to analyse differences in this variable. For the categorical variables Pearson’s
chi-square test (x
2
) was used. Differences between groups were considered as significant if
p(two-sided)B0.05. The software used was SPSS version 14.0.
Results
Sample characteristics
At the time of the data collection, the age of the participants ranged from 13 to 22 years, with
a mean age of 16.2 years [standard deviation (SD) 1.9]. Three participants were,
respectively, aged 19, 20 and 22 years. However, these somewhat older participants
had committed their offences when they were under the age of 18. The sibling offender
8I. Tidefors et al.
Downloaded By: [Goteborgs Universitetsbibliote] At: 11:13 27 May 2010
group (n21) had a mean age of 15.7 years, with a standard deviation of 2.0. The non-sibling
offender group (n24) had a mean age of 16.8, years with a standard deviation of 1.7. The
age difference was not significant.
Twenty-nine of the 45 boys had parents who were born in Sweden, five boys had one
parent born in Sweden and one parent born in another country, 11 boys had parents who were
both born in another country, and one of the boys was adopted.
Regarding intellectual difficulties (impaired learning abilities), 22 of 45 boys had no such
difficulties, whereas 20 boys were considered to have minor intellectual difficulties and three
had moderate difficulties. Of the 45 participants, 15 boys had some behavioural/acting-out
diagnosis, the most frequent of which was attention deficit hyperactive disorder (ADHD),
which was found in 10 of the boys. Furthermore, 28 boys had been victims of bullying,
whereas 16 had been bullying another child. Other antisocial behaviours found in the group
(n45) were: involvement in other criminal activities (excluding the sexual abuse), 23 boys;
drug/alcohol abuse, 13 boys; and involvement in fights (referring to documents and registers),
27 boys. There was only one significant difference between the sibling offender group and the
non-sibling offender group concerning these diagnostic and demographic variables: the
sibling offender group had been less involved in fights (x
2
(1, n45)
4.82, p0.028).
All but two of the participants had siblings in their families. The number of children in
the families (including the boy) ranged from one to 16, with a median of four. The sibling
offender group had significantly more siblings (MannWhitney U154.5, p0.023). All
the boys in the sibling offender group had younger siblings, whereas 17 of 24 in the
non-sibling offender group had younger siblings. This difference was significant (x
2
(1, n45)
7.25, p0.007).
Family dysfunction
On the six variables that were clustered together concerning family dysfunction, the sibling
offender group had a mean of 3.67 (SD 1.46), whereas the mean in the non-sibling offender
group was 2.25 (SD 1.68). The difference between the two groups was significant (t
(43)
3.00, p0.004, two-tailed). The frequencies of each separate family dysfunction variable are
displayed in Table I.
The differences between the groups were all in the expected direction, with the sibling
offenders having a higher degree of family dysfunction. Significant differences were found
considering ‘‘living in or had ever lived in a foster-home’’,‘‘victim of psychological abuse’’ and
‘‘parental substance abuse’’.
Ta b l e I . The frequencies of each separate family dysfunction variable and pr ior victimization variables (n45)
Sibling offenders (n21) Non-sibling offenders (n24)
Variable Frequency % Frequency % x
2
Physical abuse 14 67 11 46 1.97
Psychological abuse 19 90 15 63 4.75*
Divorce in the family 16 76 15 63 .98
Substance abuse 8 38 3 13 3.97*
Sexual abuse** 8 38 4 17 2.63
Child removal 12 57 6 25 4.82*
*pB0.05. **Sexual abuse perpetrated by a family member towards the boy or towards other victim/victims.
Sibling incest 9
Downloaded By: [Goteborgs Universitetsbibliote] At: 11:13 27 May 2010
History of victimization
The sibling offender group were, to a significantly higher degree, victims of psychological
abuse (see Table I). No such significance was found concerning physical abuse, but the result
was in the expected direction. Forty-eight per cent of the boys in the sibling offender group
had themselves been sexually abused compared to 33% of the boys in the non-sibling offender
group.
Severity and duration of the abuse
Almost half the boys had sexually abused more than one victim. For 16 boys the first victim
was someone in the immediate family, for 13 the first victim was a friend, neighbour or
another relative, for 15 the first victim was a stranger, and one boy’s first victim was a
stepsibling, with whom he had lived for only a short time.
In comparison to the non-sibling offenders, there was a tendency that the sibling
offenders were more likely to have abused someone younger than themselves. The mean age
difference between the abuser and the victim was 3.2 years (SD2.19) in the sibling offender
group compared to 0.2 (SD 7.23) in the non-sibling offender group (t
(43)
1.84, p0.072,
two-tailed).
Furthermore, the sibling offenders were younger at their first abuse occasion; 76% were
14 years or younger compared to 38% in the non-sibling offender group (x
2
(1, n45)
6.79,
p0.009).
A significantly larger number of sibling offenders, 19 of 21, had repeated the abuse
towards the same victim compared to the three of 24 boys in the non-sibling offender group
(x
2
(1, n45)
18.87, p0.001).
No significant differences were found between the groups concerning having abused a
same-sex victim or whether penetration had been part of the abuse.
Discussion
Several studies distinguish between different subgroups of adolescents who sexually offend.
These comparisons are made mainly between child and peer offenders (Hendriks & Bijleveld,
2004) or between solo and group offenders (Bijleveld & Hendriks, 2003). However, few studies
focus upon adolescents molesting sibling versus adolescents molesting non-siblings. The low
number of sibling studies could perhaps have something to do with the incest taboo, and the
difficulties that researchers may experience thinking beyond their own taboos (Tidefors &
Drougge, 2006). Erickson (1999) has described this paradox: ‘‘The major obstacle to studying
incest avoidance in humans has been the incest taboo’’ (Erickson 1999, p. 167).
Findings
In this study, we found differences between adolescents abusing their siblings and those
abusing non-siblings. Although not all comparative analyses showed significant differences,
they all pointed in the direction of the hypothesis, i.e. a higher degree of family dysfunction
in the sibling offender group and more previous victimizations in the sibling offender
group. Analyses of the offending behaviour and the duration of the abuse between the
groups indicated that the offending behaviour was more severe in the sibling offender group.
Furthermore, it appeared that the sibling offenders showed externalizing behaviours to a
lesser degree, as they were involved in fights less often.
10 I. Tidefors et al.
Downloaded By: [Goteborgs Universitetsbibliote] At: 11:13 27 May 2010
In both the sibling offender group and the non-sibling offender group, a majority of the
offenders had grown up in families where they had been the victims of psychological abuse.
Different forms of family dysfunction, such as psychological abuse, parental neglect and
rejection, have a negative impact on children. Sibling incest can be seen as a way to
compensate for unfulfilled emotional needs for nurture and comfort (Haskins, 2003; Salazar
et al., 2005). If sexual abuse from parents is also a part of the upbringing, the children are
introduced to a sexual world for which they are neither prepared physically nor psycholo-
gically. This too-early ‘‘introduction’’ to sexuality, and an introduction by the wrong actors,
may have the consequence of siblings beginning to use sexual behaviours as a symbol of
affection and thus sexualizing the relationship with each other, and sometimes the distinction
between victim and offender is blurred (Schwartz et al., 2006). In an early study, Marshall
and Mazzucco (1995) argued that if a child is rejected by its parents early in life this alone can
dispose for sexually abusive behaviour, and they point to the fact that the attachment system
and sexual development are closely interrelated.
Early childhood bonding is associated with a strong negative reaction to incestuous
behaviour (Fessler & Navarrete, 2004; Walter & Buyske, 2003). According to our findings, it
seems that under normal circumstances bonding between children living in the same family
leads to sexual inhibition, but bonding as a result of unfulfilled need might evoke sexuality.
Consequently, our findings were more in accordance with the results from Salazar et al.’s
(2005) finding that unavailable parents contribute to a higher degree of bonding between
siblings, and this comfort-seeking can become sexualized. Further, in families with a general
lack of limits concerning sexuality, it is possible to suppose that a limit in the form of the incest
taboo is more difficult both to establish and maintain, and this taboo is probably not strong
enough in the minds of the sibling offenders. The sibling offenders are also young, not yet
having incorporated the social codes of sexuality (Caffaro & Con-Caffaro, 2005).
Limitations
The most important limitation of this study is that we have studied only clinical cases. As
Carlson et al. (2006) point out, little is known about the consequences of sibling incest, and
what we know is built upon different clinical groups. Hence, we know little about sibling
incest survivors who are never identified clinically. However, the fact that Worling’s (1995a)
results point in the same direction as the results in the present study gives some support for
generalization of our results. Another limitation with the present study could be that data were
gathered during a period of four years. However, Swedish society has not changed in any
dramatic way during this period, so it is unlikely that the length of the data collection period
influenced the results.
Some comments should be made on the assignment of the cases into the two groups. The
non-sibling group was a mixed group, with one boy molesting a stepsibling with whom he had
lived for only a short time, two boys had molested younger children and 21 had molested
peers or adults. The sample was small, and with a larger sample it would have been possible to
compare three groups: sibling offenders, non-sibling child offenders and peer abusers. It had
also been possible to divide the sibling incest offenders into those who had molested only
siblings and those who had molested a sibling plus other children, peers or adults. Putting
these ‘‘mixed’’ cases into a third group would have made it possible to isolate the effect of
family dysfunction on sibling incest. However, as the main interest was to explore the violation
of the incest taboo the criterion was: ‘‘at least one victim had been a sibling’’. The importance
of summarizing the results of many studies with smaller sample sizes, as well as studies built
from different groups, both clinical and non-clinical, should be stressed.
Sibling incest 11
Downloaded By: [Goteborgs Universitetsbibliote] At: 11:13 27 May 2010
Further, this study has focused upon background variables at individual and family
levels, but it is reasonable to study sexually abusive behaviour from a multifactor perspective,
focusing upon interaction between the individual and family as well as at community level.
Conclusion
A higher degree of family dysfunction was found in the sibling offender group and more
previous victimization was found in the sibling offender group. Although the results showed
differences between the sibling offender group and the non-sibling offender group regarding
aspects of family dysfunction, these aspects cannot be seen as causative of whether or not an
adolescent sexual offender will abuse a sibling. It can merely suggest indications of such a
relation. This is also true for whether abusing a sibling, as opposed to abusing a neighbour,
friend or a stranger, can be said to predict more severe offending behaviour. However, the
differences in the present study all pointed in the same direction, and suggestions can be made
about a stronger relation between having been victimized previously, physically, psychologi-
cally or sexually, and becoming a sibling offender. Sexual abuse cannot be the result of a single
factor, but rather the consequences of interactions among many factors. There is a need for
more research to examine possible pathways from different background factors to different
sexual offending behaviours.
As in this study, many studies on adolescents who sexually offend are built upon small
samples. If results from studies in different countries point in the same direction, indicating no
significant cultural differences, international cooperation could allow the collection of larger
samples. Larger international samples could, on the other hand, provide valuable knowledge
about interesting cultural differences. Such cooperation would make generalizations to a
larger population possible and enable research on the differences in social contexts which may
decrease or increase sibling incest.
Because a higher proportion of children and teenagers today are living in stepfamilies,
probably with a weaker taboo against sibling incest, it is important to distinguish well-
functioning stepfamilies from those with adults not capable of having the children’s
perspective and best interests in focus.
References
Adler, N. A., & Schutz, J. (1995). Sibling incest offenders. Child Abuse and Neglect,19,811819.
Aoki, K. (2005). Avoidance and prohibition of brothersister sex in humans. Society of Population Ecology,47,1319.
Ascherman, L. I., & Safier, E. J. (1990). Sibling incest: A consequence of individual and family dysfunction. Bulletin of
the Menninger Clinic,54,311322.
Barbaree, H. E., & Langton, C. M. (2006). The effects of child sexual abuse and family environment. In H. E. Barbaree
& W. L. Marshall (Eds), The juvenile sex offender, (2nd edn) (pp. 5876). New York: Guilford Press.
Barbaree, H. E., & Marshall, W. L. (2006). An introduction to the juvenile sex offender: Terms, concepts, and
definitions. In H. E. Barbaree & W. L. Marshall (Eds), The juvenile sex offender, (2nd edn) (pp. 118). New York:
Guilford Press.
Bass, L. B., Taylor, B. A., Knudson-Martin, C., & Huenergardt, D. (2006). Making sense of abuse: Case studies in
sibling incest. Contemporary Family Therapy,28,87109.
Becker, J. V., Kaplan, M. S., Cunningham-Rathner, J., & Kavoussi, R. (1986). Characteristics of adolescent incest
sexual perpetrators: Preliminary findings. Jour nal of Family Violence,1,8597.
Bevc, I., & Silverman, I. (2000). Early separation and sibling incest: A test of the revised Westermarck theory. Evolution
and Human Behavior,21,151161.
Bijleveld, C. C. J. H., & Hendriks, J. (2003). Juvenile sex offenders: Differences between group and solo offenders.
Psychology, Crime and Law,9,237245.
12 I. Tidefors et al.
Downloaded By: [Goteborgs Universitetsbibliote] At: 11:13 27 May 2010
Caffaro, J. V., & Conn-Caffaro, A. (2005). Treating sibling abuse families. Aggression and Violent Behavior,10, 604
623.
Carlson, B. E., Maciol, K., & Schneider, J. (2006). Sibling incest: Reports from forty-one survivors. Journal of Child
Sexual Abuse,15,1934.
Cyr, M., Wright, J., McDuff, P., & Perron, A. (2002). Intrafamilial sexual abuse: brothersister incest does not differ
from fatherdaughter and stepfatherstepdaughter incest. Child Abuse and Neglect,26, 957973.
deMause, L. (1974). The history of childhood . New York: Psychohistory Press.
deMause, L. (1991). The universality of incest. The Journal of Psychohistory,19,123164.
Diggs, S. (1997). The plural taboo. Journal of Analytical Psychology,42, 459479.
DiGiorgio-Miller, J. (1998). Sibling incest: Treatment of the family and the offender. Child Welfare,77,335346.
Erickson, M. T. (1999). Incest avoidance. Clinical implications of the evolutionary perspective. In W. R. Trevathan,
E. O. Smith & J. J. McKenna (Eds), Evolutionary medicine (pp. 165181). New York, Oxford: Oxford University
Press.
Fessler, D. M. T., & Navarrete, I. (2004). Third-party attitudes toward sibling invest. Evidence for Westermarck’s
hypotheses. Evolution and Human Behavior,25, 277294.
Finkelhor, D. (1979). Sexually victimized children. New York: Free Press.
Graham-Bermann, S. A., & Cutler, S. E. (1994). The brothersister questionnaire: Psychometric assessment and
discrimination of well-functioning from dysfunctional relationships. Journal of Family Psychology,8,224238.
Hardy, M. S. (2001). Physical aggression and sexual behavior among siblings: A retrospective study. Journal of Family
Violence,16, 255268.
Haskins, C. (2003). Treating sibling incest using a family systems approach. Journal of Mental Health Counseling,25,
337350.
Hendriks, J., & Bijleveld, C. C. J. H. (2004). Juvenile sexual delinquents: Contrasting child abusers with peer abusers.
Criminal Behaviour and Mental Health,14,238250.
Immerman, R. S., & Mackey, W. C. (1997). An additional facet of the incest taboo: A protection of the mating-strategy
template. Journal of Genetic Psychology,158, 151164.
Inger, G. (1986). Svensk ra
¨ttshistoria [Legal History in Sweden]. Stockholm: Liber.
Kahr, B. (1991). The sexual molestation of children: Historical perspectives. Jour nal of Psychohistory,19,191214.
Kilborne, B. (2003). Oedipus and the oedipal. American Jour nal of Psychoanalysis,63,289297.
Lloyd, J. (1982). The management of incest: An overview of three inter-related systems*the family, the legal and the
therapeutic. Journal of Social Welfare Law,4,1628.
Marshall, W. L., & Mazzucco, A. (1995). Self-esteem and parental attachments in child molesters. Sexual Abuse: A
Journal of Research and Treatment,7,279286.
Mendel, M. P. (1995). The made survivor. The impact of sexual abuse. Newbury Park: Sage.
Miranda, A. O., & Corcoran, C. L. (2000). Comparison of perpetration characteristics between male juvenile and
adult sexual offenders: Preliminary results. Sexual Abuse: A Journal of Research and Treatment,12, 179188.
Nyman, A., & Svensson, B. (1995). Pojkmottagningen. Sexuella O
¨vergrepp och Behandling [The Boy Consulting Room.
Sexual Assault and Treatment]. Stockholm: Ra
¨dda Barnen.
O’Brien, M. J. (1991). Taking sibling incest seriously. In M. Patton (Ed.), Family Sexual Abuse: Frontline Research and
Evaluation (pp. 7592). Newbury Park, CA: Sage Publications.
Parker, H., & Parker, S. (1986). Fatherdaughter sexual abuse: an emerging perspective. American Journal of
Orthopsychiatry,56, 531549.
Parker, S. (1996). Full brothersister marriage in Roman Egypt: Another look. Cultural Anthropology,11(3), 362376.
Perlmutter, H. L., Engel, T., & Sager, J. C. (1982). The incest taboo: Loosened sexual boundaries in remarried
families. Journal of Sex and Mar ital Therapy,2,8396.
Phillips-Green, M. J. (2002). Sibling incest. Family Journal: Counseling and Therapy for Couples and Families,10,
195202.
Pierce, L. H., & Pierce, R. L. (1987). Incestuous victimization by juvenile sex offenders. Journal of Family Violence,4,
351365.
Rudd, J. M., & Herzberger, S. D. (1999). Brothersister incestfatherdaughter incest: A comparison of characteristics
and consequences. Child Abuse and Neglect,23,915928.
Salazar, L. F., Camp, C. M., DiClemente, R. J., & Wingood, G. M. (2005). Sibling incest offenders. In T. P. Gullotta
& G. R. Adams (Eds.), Adolescent Behavioral Problems (pp. 503518). New York: Springer Science.
Scheidel, W. (1996). Brothersister and parentchild marriage outside royal families in ancient Egypt and Iran: A
challenge to the sociobiological view of incest avoidance? Ethology and Sociobiology,17, 319340.
Schwartz, B. K., Cavanaugh, D., Pimental, A., & Prentky, R. (2006). Descriptive study of precursors to sex offending
among 813 boys and girls: Antecedent life experiences. Victims and Offenders,1,6166.
Sibling incest 13
Downloaded By: [Goteborgs Universitetsbibliote] At: 11:13 27 May 2010
Seto, M. C., Murphy, W. D., Page, J., & Ennis, L. (2003). Detecting anomalous sexual interest in juvenile sex
offenders. Annals of the New York Academy of Sciences,989,118130.
Shaw, J. A., Lewis, J. E., Loeb, A., Rosado, J., & Rodriguez, R. (2000). Child on child sexual abuse: Psychological
perspectives. Child Abuse & Neglect,12, 15911600.
Smith, H., & Israel, E. (1987). Sibling incest: A study of the dynamics of 25 cases. Child Abuse and Neglect,11,
101108.
Studer, L. H., & Aylwin, A. S. (2006). Sexual offender subtyping: The incest offender question. Sexual Offender
Treatment, 1. Retrieved January 14, 2009, from http://www.sexual-offender-treatment.org/42.0.html
Tidefors, I., & Drougge, M. (2006). The difficulties in understanding the role of sexuality in sexual abuse towards
children: In-depth interviews with perpetrators. Inter national Journal of Qualitative Studies on Health and Well-being,
1, 178187.
Turner, A. P. (2008). Incest, inbreeding, and intrafamilial conflict: Analyzing the boundaries of sexual permissiveness
in modern North Africa. Sexuality and Culture,12,3844.
Walter, A., & Buyske, S. (2003). The Westermarck effect and early childhood co-socialization: Sex difference in
inbreeding-avoidance. British Journal of Developmental Psychology,21, 353365.
Wasserman, S., & Rosenfeld, A. (1992). An overview of the history of child sexual abuse and Sigmund Freud’s
contributions. In W. O’Donohue & J. H. Geer (Eds), The sexual abuse of children: Theor y and research, vol. I
(pp. 4972). Mahwah, NJ: Lawrence Erlbaum Associates.
Worling, J. R., & Curwen, T. (2000). Adolescent sexual offender recidivism: Success of specialized treatment and
implications for risk prediction. Child Abuse and Neglect,24, 965982.
Worling, J. R. (1995a). Adolescent sibling-incest offenders: Differences in family and individual functioning when
compared to adolescent nonsibling sex offenders. Child Abuse and Neglect,19,633643.
Worling, J. R. (1995b). Sexual abuse histories of adolescent male sex offenders: Differences on the basis of the age and
gender of their victims. Journal of Abnor mal Psychology,104, 610613.
Worling, J. R. (2001). Personality-based typology of adolescent male sexual offenders: Differences in recidivism rates,
victim-selection characteristics, and personal victimization histories. Sexual Abuse: A Journal of Research and
Treatment,3,149166.
14 I. Tidefors et al.
Downloaded By: [Goteborgs Universitetsbibliote] At: 11:13 27 May 2010
