Adverse childhood experiences and psychosocial functioning problems for youths who sexually harm siblings

ABSTRACT

This study explores adverse childhood experiences and problematic psychosocial functioning for youths who exhibit harmful sexual behaviours (HSBs) against siblings in comparison to those that sexually harm non-siblings. In a sample of Australian male adolescents referred to a specialised sexual offending treatment service, greater prevalence of all adverse experiences investigated, except for caregiver incarceration, was found for youths who harmed siblings. Youths whose sexual behaviours harmed siblings were differentiated from other youths with HSBs in regard to characteristics of caregivers, including caregiver mental health issues, caregiver sexual victimisation experiences, and instability in caregivers during childhood. In addition, youths who exhibited HSBs against siblings experienced a greater total number of adversities in their lives and were characterised by poorer psychosocial functioning, such as social exclusion and internalising problems. Implications of these findings for clinical treatment is discussed.

PRACTICE IMPACT STATEMENT

This research identifies developmental risk factors of youths who exhibit HSBs against siblings and examines if and how these differ from characteristics of youths who sexually harm non-siblings. Greater understanding of youths who sexually harm siblings allows treatment and prevention strategies to be tailored to their specific needs.

KEYWORDS:

• youth harmful sexual behaviours
• sibling abuse
• adverse childhood experiences
• maltreatment
• sexual harm risk factors

1. Introduction

1.1. Youth who exhibit sexual harm towards siblings

The harm caused by childhood sexual abuse has long been acknowledged, with physical, emotional and psychological consequences that frequently endure throughout the life course (Carretier et al., 2022; Cyr et al., 2002; Krienert & Walsh, 2011). These consequences are often exacerbated in circumstances where harm is perpetrated by a sibling, due to feelings such as confusion around responsibility and shame experienced by victims (McDonald & Martinez, 2017; Tener et al., 2020). Sibling sexual harm (and its discovery) has long-lasting effects on sibling relationships, as well as relationships with the immediate and extended family unit, with those who are harmed frequently distancing themselves (both physically and emotionally) from their families of origin, and those who perpetrate harm often excluded from the family unit (Ballantine, 2012; Caffaro & Conn-Caffaro, 2005; Grant et al., 2009).

Establishing the prevalence of sibling HSBs is a difficult task for numerous reasons, including variation in how the concepts of siblings and harmful sexual behaviour are defined, and the underreporting of this form of harm (Caffaro & Conn-Caffaro, 2005; Carlson et al., 2006; Krienert & Walsh, 2011). Sibling abuse is the most common type of child sexual harm (McCoy et al., 2022), as well as the most common type of intrafamilial sexual harm, with evidence of it occurring two to five times more often than father-daughter incest in some cases (Ballantine, 2012; Carretier et al., 2022; Krienert & Walsh, 2011; Latzman et al., 2011; McDonald & Martinez, 2017; Tener et al., 2020). When considering youth who exhibit sexual harm, estimates of intrafamilial HSBs vary. For example, Martijn et al. (2020) state that approximately a quarter of the sexual harm perpetrated by North American adolescents is against a relative, while other studies suggest that up to half of HSBs perpetrated by adolescents involve harm to siblings (Latzman et al., 2011; Shaw, 1999).

The prevalence of sexual harm against siblings, alongside the consequences of experiencing such harm, reinforces the need to understand factors associated with these behaviours. A dearth of research on sibling sexual abuse however, limits understanding of this phenomenon, creating barriers for effective prevention and intervention (Carretier et al., 2022; Martijn et al., 2020; McCoy et al., 2022). Further knowledge of the ways in which developmental risk factors differ for youths who sexually harm siblings, compared to those who harm non-siblings, will inform treatment efforts as well as prevention strategies for this population.

1.2. Developmental risk factors associated with youth HSBs against siblings

Some preliminary developmental risk factors have been identified in the literature for youths who sexually harm siblings. These factors reflect the individual functioning of young people who exhibit HSBs, their own traumatic experiences, and the family environments in which they exist.

1.2.1. Family dysfunction

Families in which sibling sexual harm occurs are frequently described as dysfunctional and chaotic (Ballantine, 2012; Grant et al., 2009; Joyal et al., 2016). Caregivers of youths who sexually harm siblings often employ poor child-rearing techniques, with low levels of parental involvement and inappropriate supervision (Cyr et al., 2002; McCoy et al., 2022; Tener et al., 2020). In addition to affecting parent–child bonds (Thornton et al., 2008), these dysfunctional influences increase opportunity for sexual harm to occur (McDonald & Martinez, 2017; Tidefors et al., 2010). Further, parents of youths with intrafamilial HSBs frequently experience difficulty in enforcing rules and regulations in the household (Thornton et al., 2008), resulting in discipline methods which include verbal and physical abuse being commonly employed (Cyr et al., 2002).

Relationships within the family units of youths who sexually harm siblings feature ineffective family communication styles and poor conflict resolution (Thornton et al., 2008). These dysfunctional relationships are frequently characterised by marital discord that often results in young people being exposed to family violence (Ballantine, 2012; Joyal et al., 2016; Latzman et al., 2011). Consistent with social modelling theories, exposure to violence in the home may reinforce the use of coercive or aggressive strategies used to engage in abusive behaviours (McDonald & Martinez, 2017).

1.2.2. Maltreatment

Childhood maltreatment experiences (e.g. neglect, physical and emotional abuse) have long been noted in the developmental histories of young people who engage in offending behaviours, with the prevalence shown to be greater amongst youths who exhibit HSBs, compared to those who perpetrate non-sexual violent harm (Levenson et al., 2017; Ogilvie et al., 2022). Given the more serious family dysfunction noted for youths who sexually harm siblings, it is not surprising that incidences of maltreatment are frequently observed amongst perpetrators of sibling HSB (Grant et al., 2009). For example, in Carlson et al.’s (2006) study of 41 adult survivors of childhood sibling sexual abuse, close to half (45%) of the sample reported having experienced physical abuse, and over three quarters (78%) reported emotional abuse by a family member. Neglect has also been highlighted as influential, with research suggesting that older children may harm younger siblings in an attempt to satisfy unmet emotional needs (Tidefors et al., 2010).

In particular, high rates of sexual victimisation have been found amongst youths who sexually harm siblings, with prevalence exceeding that found amongst youths that exhibit HSBs against non-siblings (Joyal et al., 2016; Latzman et al., 2011). Some young people that have experienced sexual abuse process their trauma by displaying developmentally inappropriate and/or problematic sexual behaviours in addition to, or instead of exhibiting sibling sexual harm (Rayment-McHugh & Nisbet, 2003).

Not only are youths who sexually harm siblings more likely to have themselves experienced sexual abuse, but the literature also suggests intergenerational patterns, where those who exhibit sibling sexual harm frequently have parents who were themselves victimised by physical and sexual abuse during childhood (Ballantine, 2012; Grant et al., 2009). This intergenerational trauma was noted in Cyr et al.’s (2002) study, where 61% of siblings sexually harmed by a brother had a mother who had experienced sexual victimisation as a child. Similarly, Smith and Israel (1987) found that 72% of mothers and/or fathers of young people who sexually harmed a sibling had experienced sexual abuse themselves. In O’Brien’s study, 36% of mothers and 10% of fathers of those that sexually harmed siblings had themselves experienced childhood sexual abuse, compared to 9.1% of mothers and 5.5% of fathers of youths who exhibited extrafamilial sexual harm.

1.2.3. Psychosocial functioning

Childhood adversities such as maltreatment and family dysfunction have been demonstrated to significantly impact several domains of psychosocial functioning, which increases the risk of poor outcomes, including youth involvement in harmful sexual and non-sexual behaviours (Goldenson et al., 2021; Levenson et al., 2017; Ogilvie et al., 2022). Psychosocial deficits such as poor social functioning are noted amongst youths that exhibit HSBs in general (Thornton et al., 2008). For those that sexually harm siblings, poor social functioning is theorised to provide a mechanism through which inappropriate sexual behaviours emerge, by limiting participation in age-appropriate relationships, resulting in adolescents pursuing intimacy with younger children and/or through forcible means (Martijn et al., 2020; Worling, 2001). Accordingly, some research identifies deficits in social skills and/or interpersonal relationships for youths who engage in sibling HSBs (Grant et al., 2009). Findings are mixed however, as to whether youths who harm siblings are more likely than other types of youths with HSBs to experience deficits in social functioning. For example, Worling (2001) categorised adolescent males convicted for sexual harm based on self-reported responses on the California Personality Inventory, and found that only 20% of youths categorised as unusual/isolated had sexually harmed a sibling, compared to 42% of youths categorised as antisocial/impulsive and 37% of youths categorised as confident/aggressive.

Poor mental health is frequently observed in the general population of youths that exhibit HSBs For example, Hunter et al. (2003) found that close to half of a sample of youths who sexually harmed children experienced depression and anxiety at levels suggesting the need for intervention. Grant et al. (2009) suggests that internalising disorders and related symptomology may be particularly relevant for those who sexually harm siblings however these factors have not been sufficiently investigated in research to draw firm conclusions. Externalising behaviours on the other hand, such as delinquency, substance use, and other (non-sexual) offending behaviours are often theorised to occur less frequently amongst those with sibling-directed HSBs. O'Brien (1991) found lower rates of crimes against persons for those that sexually harmed siblings than other youths with HSBs and suggests that the typical use of force, coercion and violence found with sexual harm perpetrated against non-related peers and adults better aligns with general offending behaviours than strategies employed by those who sexually harm siblings. Indeed, research finds those with intrafamilial HSBs to be less antisocial in general than those with extrafamilial HSBs (Martijn et al., 2020; Seto et al., 2015). There is no consensus within research comparing mental health of youths with HSBs exhibited against siblings and non-siblings, with some studies finding no differences, and others having conflicting results as to whether externalising and antisocial behaviours are more commonly a feature of those who sexually harm siblings or those who sexually harm non-siblings,

1.3. Studies comparing youths who sexually harm siblings and non-siblings

The findings above are echoed within the limited body of research specifically investigating differences in developmental risk factors for youths who sexually harm siblings, compared to those who harm non-siblings. In general, these studies find that youths with sibling-directed HSBs more often experience forms of maltreatment and greater family dysfunction than other youths who sexually harm. Findings relating to psychosocial functioning are less conclusive.

An early study by O'Brien (1991) drew comparisons between 50 youths who sexually harmed a sibling, 57 youths who sexually harmed a non-sibling, and 38 youths who sexually harmed a peer and/or adult. Young people with sibling-directed HSBs were found to have more experiences of sexual and physical victimisation and more often lived in families that clinicians rated as “severely disturbed”. Close to two thirds of youths who sexually harmed a sibling were categorised by clinicians as undersocialised, defined as having poor social skills and few or no peer-aged friends. In addition to their HSBs, those who harmed siblings were also more likely to be rated by parents as exhibiting problem behaviours often seen with conduct disorder diagnoses. These findings of increased behavioural problems amongst youths who sexually harm siblings do not align with later research findings, however the source of the information (i.e. parent reports) may play a role in this.

Worling (1995) examined differences in a sample of 32 youths with HSBs exhibited against a sibling compared to 28 who sexually harmed a non-sibling and found greater rates of family dysfunction and sexual abuse experiences amongst those with sibling-directed HSBs. Specifically, youths who sexually harmed siblings more often reported dissatisfying family environments characterised by marital discord, as well as poor relationships with caregivers, parental rejection, and harsh physical discipline. In addition, significantly more youths who harmed siblings than those who harmed non-siblings reported a history of sexual victimisation. When comparing individual psychological functioning however, no significant differences were found in levels of self-esteem, depression, hostility, and aggression, or in regard to social acceptance.

Rayment-McHugh and Nisbet’s (2003) comparison of 10 youths with HSBs exhibited against siblings and 10 youths with HSBs exhibited against non-siblings also found no significant differences in psychological functioning according to Youth Self Report (YSR) scores for internalising and externalising problem behaviours, social problems, and feelings of anxiety and depression. When parenting practices were examined, the authors found significant differences in positive parenting behaviours, but not in parental monitoring or involvement, nor in inconsistent or harsh discipline practices. This study utilised a particularly small sample however, which may have affected generalisability of trends found within the data.

In Tidefors et al.’s (2010) study, offending and family characteristics of 21 adolescents who sexually harmed siblings were compared to 24 youths who harmed non-siblings, all receiving treatment at a psychiatric clinic. In general, those with sibling-directed HSBs were found to have more dysfunctional family environments – this included significantly higher rates of psychological abuse and substance-use by a parent, as well as a greater likelihood of a child being removed from the family by child protective services. While sexual abuse (defined in this study as a household in which a family member had perpetrated sexual harm against the adolescent themselves, or some other) was more prevalent amongst youths who sexually harmed siblings, this difference was not significant.

In a sample of male adolescents in a US residential treatment programme, Latzman et al. (2011) compared 100 youths with HSBs against siblings to 66 youths with HSBs against non-siblings, and found significantly greater proportions of youths who sexually harmed siblings had experienced sexual abuse (although not physical or emotional abuse, or neglect). No significant differences were found in the Youth Level of Service/Case Management Inventory (YLS/CMI) Family Circumstances/Parenting subscale, or in the ERASOR Family/Environmental Functioning subscale, both of which provide measures of general poor parenting. Significantly greater prevalence of exposure to domestic violence was found for youths with sibling-directed sexual harm however, as was exposure to pornography. The authors concluded that these factors demonstrate differences in more aggressive family dysfunction.

Most recently, Joyal et al. (2016) examined archival records of adolescents with HSBs serviced by a Canadian legal forensic centre and compared characteristics of 61 youths who had sexually harmed a biologically related brother or sister, with 122 youths who had harmed an extrafamilial child and 142 youths who had harmed an extrafamilial peer/adult. Youths with sibling-directed HSBs were found to have significantly higher rates of sexual and physical victimisation experiences than those whose harm was against an extrafamilial child or peer/adult. When social functioning was examined, youths who sexually harmed siblings were more likely to be socially isolated than those who sexually harmed extrafamilial peers or adults, but less likely to experience such social rejection as youths who sexually harmed extrafamilial children. In general, youths who exhibited HSBs against siblings tended to be less antisocial in nature, with a greater prevalence of delinquency characteristics such as delinquent peer associations, Conduct Disorder diagnoses, and substance use found amongst those who sexually harmed extrafamilial peer/adult victims.

Studies of intrafamilial sexual harm, although not restricted to those who harm against siblings only, provide further insight into factors related to HSBs against child relatives. Seto et al. (2015) conducted a meta-analysis of 78 independent samples of adults with HSBs and showed that those that perpetrated intrafamilial sexual harm had more often experienced abuse (including sexual victimisation) and neglect, as well as poor attachment bonds (to mothers in particular). In contrast, those who perpetrated extrafamilial sexual harm tended to be more antisocial, with self-regulation issues, antisocial attitudes, and greater engagement with negative peer groups, which likely contributed to their more extensive criminal histories. Seto et al. also found that those with intrafamilial HSBs were less likely than those with extrafamilial HSBs to experience interpersonal problems, be lonely, or lack successful romantic relationships.

While Seto et al. (2015) did not focus exclusively on youth who offend, Martijn et al. (2020) extended this research to examine characteristics of male adolescents with HSBs based on 28 independent samples. The study found more extensive histories of child maltreatment, more severe family dysfunction, and greater prevalence of internalising disorders amongst youths who exhibited intrafamilial sexual harm. In contrast, youths with intrafamilial HSBs were less likely than those with extrafamilial HSBs to exhibit antisocial behaviours and attitude, associate with delinquent peers, or engage in substance use and abuse.

1.4. Adverse Childhood Experiences (ACEs)

Many of the maltreatment and family dysfunction risk factors found to be prevalent amongst youth who sexually offfend are captured in Felitti et al.'s (1998) ACEs conceptualisation, which provides a useful framework for exploring developmental risk factors for youths who exhibit sexual harm. The original 10 item ACE scale included three items related to abuse (physical, emotional, and sexual); two items related to neglect (physical and emotional) and five items reflecting household dysfunction (parental separation/ divorce, residing with a family member with mental illness, substance abuse or a history of incarceration, and domestic violence within the household).

Recent research has examined ACEs amongst people who engage in offending behaviours, with findings suggesting a relationship between early adversity and later antisocial behaviour and crime that is even more apparent for youths with HSBs (Levenson et al., 2017; Ogilvie et al., 2022). For example, DeLisi et al. (2017) found that risk of perpetrating sexual harm increased in line with the number of ACEs, and Craig and Zettler (2021) found that the number of ACEs experienced affected the likelihood of rearrest for crimes of domestic violence and sexual assault. More recently, Ogilvie et al. (2022) found that all ACEs except caregiver offending (incarceration) were more prevalent amongst youths convicted for sexual offences than those convicted for violent and non-violent offences. Further, youths convicted for sexual offences experienced a higher mean number of ACEs than these other offending cohorts.

While ACEs have been demonstrated to be more prevalent for youths who exhibit HSBs little research has examined differences in ACEs for specific cohorts of youths who sexually harm, such as those who sexually harm siblings. In particular, the cumulative effect of childhood adversities for young people who sexually harm siblings has not been explored. This makes the ACEs framework a useful tool for examining differences in developmental risk factors for youths with HSBs against siblings and non-siblings.

1.5. Aims of the current study

The aims of this study are to increase knowledge of the characteristics of male youth who engage in HSBs against siblings. The research examines typological differences in youths with HSBs by exploring whether adverse experiences and concomitant psychological functioning in the developmental histories of male adolescents convicted of sexual harm against siblings differs from those who harm non-siblings. Given recent research highlighting the prevalence of ACEs in the developmental histories of youths with HSBs, an ACEs framework is employed in the examination of these risk factors. Differences in both specific adversities experienced, as well as the total number of ACEs experienced are examined, alongside related problems in psychological functioning.

2. Materials and methods

This research utilised data from a sample of young people referred to the Griffith Youth Forensic Service (GYFS) following perpetration of sexual harm. GYFS is a Griffith University and Queensland Government partnership that provides specialised services in assessment and treatment for young people across the state of Queensland who have been referred by the Department of Children, Youth Justice and Multicultural Affairs (DCYJMA) following conviction for sexual offences. GYFS clientele are frequently youths with complex needs, whose offending ranks as highly serious in the spectrum of youth sexual harm.

As part of the service delivery process, GYFS clinicians maintain detailed clinical files which include collateral information sourced through multiple sources. These files include demographic information, histories of contact with Child Safety and Youth Justice, results from psychological assessments, and details of the victim/s, the offence/s, and associated offending behaviours. In addition, clinical interviews with young people and their families yield information related to the developmental histories of youths (including experience of ACEs) that is summarised in clinical files. Information from these clinical files was coded by research assistants and entered into a database which was used for analyses in this study. All youths receiving services from GYFS are asked for active consent to utilise information from case files in research projects – ethical approval to use this information for research has been granted by Griffith University’s Human Research Ethics Council (GU ref no. 2017/565).

2.1. Participants

The sample used for this study was a cohort of 218 male adolescents referred to the Griffith Youth Forensic Service (GYFS) between 2001 and 2019 following conviction for perpetrating a sexual offence. The sample was divided into those youth who perpetrated sexual harm against a sibling (n = 63) and against a non-sibling (n = 155). Youths in the sample were aged between 12 and 19 at the time they commenced contact with GYFS, with a mean age of 16.17 years (SD = 1.34). While females with sexual offences are referred to GYFS, this study included only male participants as these make up the majority (over 95%) of GYFS clients.

Where information regarding ethnicity of clients was available (91.3% of the sample), just over half (56.0%) of participants identified as Anglo-Australian, with small numbers of youths coming from a variety of ethnic backgrounds. Around a third (34.0%) of clients who reported their cultural heritage (87.6%) identified as Aboriginal and/or Torres Strait islander.

2.2. Measures

2.2.1. Independent variables

2.2.1.1. Offending information

Details of sexual offences were extracted from official records, and included types of offences committed, setting and specific locations of offences, victim details (including number of victims, age and gender of victim/s, and relationship of victim/s to perpetrator. In addition, details of any non-sexual offending were recorded, based on Youth Justice offending histories).

2.2.1.2. Adverse Childhood Experiences (ACEs)

The current research adopted a methodological framework that included adverse experiences noted in the literature to be associated with increased likelihood of involvement in harmful sexual behaviours. Presence or absence of these adversities in the developmental histories of young males referred to GYFS was assessed using information extracted and coded from client clinical files. For each ACE item, a score of 1 was assigned where case files contained convincing evidence confirming the presence of the adversity in the young person’s history. Where the risk factor was not noted in the case file, or where the risk was suspected but there was insufficient evidence to confirm, the case was assigned a score of 0.

Felitti et al.’s (1998) model was utilised as the initial framework for examining ACEs. This model includes 10 items related to abuse (emotional, physical, and sexual); neglect (emotional and physical); and family dysfunction (parental separation or divorce; exposure to violence; exposure to a family member with a mental health illness, substance abuse issues, or who has been incarcerated). As data in the present research was drawn from client files rather than self-report surveys, some adaptations to items were required where information necessary to assess ACEs was lacking. For example, Felitti’s sixth ACE records experiences of parental separation or divorce, however, the current data set did not include this record, rather a related item, single-parent living environment was used to represent this ACE. While Felitti examined substance use (ACE 8) or mental health problems (ACE 9) of a family member, our study restricted this item to include only caregivers. Finally, often client files did not discriminate between emotional and physical neglect, therefore these ACEs were combined to create a single neglect item, resulting in nine total ACEs. Detailed item descriptions and comparisons to Felitti’s original ACEs are provided in Appendix 1.

In addition to the nine ACEs identified by Felitti et al. (1998), the current study extended experiences of adverse events during childhood to include additional risk factors noted in the literature on youths with HSBs. Caregiver inconsistency was added to capture instability of living situations during the first 12 years of the young person’s life, and was endorsed where two or more changes in caregiver (for a period of at least 6 months) occurred. To assess the effects of intergenerational sexual harm experiences, an item recorded where the young person’s caregiver was themself a victim of sexual abuse.

In addition, given evidence of poor social functioning within populations of youths with HSBs, three items concerning social isolation were included. A social isolation item was endorsed where young persons were noted under the age of 12 to lack age-appropriate friendships, not engage with peers, or experience peer rejection, and bullying victimisation indicated evidence of ongoing bullying behaviours towards the young person in the school environment. Poor social interaction reflected a lack of active participation in group or structured social activities. A total ACE score was calculated by summing the number of endorsed adverse experiences, to produce a score ranging from 0 to 14.

2.2.1.3. Psychological functioning

Given its frequent association with ACEs, psychological functioning of the young person was assessed, including where youths had exhibited internalising problems, such as anxiety, depressed feelings or nervousness; externalising problems, such as outbursts, acts of aggression, non-compliance, or self-regulation issues. Data was also collected on substance use, and early sexual behaviour problems including acts such as inappropriate touching of self or others, and sexualised talk or behaviours that occurred before the age of 10.

2.2.2. Dependent variable

2.2.2.1. Sibling sexual harm

This study compared a cohort of youths whose sexual harm was perpetrated against siblings, to a cohort whose sexual harm was against non-siblings. Victims were considered a sibling where they were biologically related to the young person that perpetrated the HSB (including half brothers and sisters) or where they were step-brothers or sisters with whom he resided. Youths who sexually harmed siblings were categorised as having perpetrated sibling-directed HSBs regardless of whether they had also (either previously or concurrently) sexually harmed non-siblings also. That is, the sibling HSB cohort was not restricted to adolescents that only sexually harmed siblings, but captured those who had ever sexually harmed a sibling.

2.3. Analyses

Given the dearth of research exploring sibling sexual harm perpetrated by youths, analyses were largely exploratory. The prevalence of adversities in the developmental histories of young males convicted of HSBs against siblings is first presented. Differences in experiences of adverse childhood events and poor psychological wellbeing for youths with HSBs against siblings was compared to those with HSBs against non-siblings using MANOVA and Chi-square tests to assess significant differences. Differences in composite ACE scores were assessed with a t-test. SPSS version 27 was used for all analyses.

3. Results

3.1. Characteristics of male youth who sexually harm siblings

In total, the sibling HSB cohort encompassed 63 youths whose age at treatment start ranged from 13 to 19 years (M = 16.08). No significant differences in ages were found between youths whose HSBs were directed toward sibling and non-siblings. The cohort of youths who sexually harmed siblings contained a significantly smaller proportion (χ² = 14.17, p < .001, ϕ_c = .272) of Indigenous young people however (13.21% Aboriginal or Torres Strait Islander; 86.79% non-Indigenous), when compared to the non-sibling victim cohort (42.01% Aboriginal or Torres Strait Islander; 57.97% non-Indigenous). A quarter (25.0%) of the sibling HSB cohort had previous contact with the Youth Justice (YJ) system before referral to GYFS, in comparison to 45.4% of the non-sibling HSB cohort. In both cases, previous YJ contact was most often for non-sexual offending (94.6% of sibling HSB cohort and 94.3% of non-sibling HSB cohort).

Youths who sexually harmed siblings were most frequently convicted for Indecent Treatment of a Child (82.5% of charges) and/or rape (69.8% of charges). As with the non-sibling HSB cohort, harmed siblings were most often female, with one in five being male. Ages of siblings sexually harmed ranged from 1 year old to 16 years (M = 8.4; SD = 2.93), except for one sibling aged 20 years. In all but three of the 63 offences, the young person was the sole perpetrator of sexual harm against his sibling. Unsurprisingly, given sibling HSB, offences most often (93.7%) occurred within the home, and only four youths perpetrated harm in a public setting. Just over half (54.0%) of offences that occurred within a domestic setting took place in a bedroom belonging to either the youth that perpetrated sexual harm, or the individual that was harmed.

3.2. Differences in ACEs for male youth who sexually harm siblings and nonsiblings

Consistent with recent research, adverse experiences were prevalent in the lives of youths who sexually harmed both siblings and non-siblings, and occurred at rates which exceeded not only the general population, but also populations of youths with non-sexual offences (Levenson et al., 2017; Ogilvie et al., 2022). In general, ACEs were noted to occur more frequently for young males who sexually harmed siblings compared to those with non-sibling HSBs.

Differences in ACEs were first assessed within the domains of maltreatment (emotional abuse, physical abuse, sexual abuse, neglect), family functioning (single parent family, exposure to DFV, caregiver substance use, caregiver mental health problems, caregiver incarceration, caregiver inconsistency, caregiver victim of sexual abuse), social exclusion (i.e. social isolation, bullying victimisation, poor social interaction) using MANOVA (see Table 1).

Table 1. ACE prevalence for males who sexually harmsiblings and non-siblings.

	Sibling sexual harm (SSH) n = 63	Non-sibling sexual harm (NSSH) n = 155	χ^2	p	ϕc
	n (%)	n (%)
Maltreatment			F = 3.880	.050	${\eta }_p^2$ =.019
Emotional abuse	32 (50.79)	62 (40.00)
Physical abuse	36 (57.14)	70 (45.16)
Sexual abuse	23 (36.51)	38 (24.52)
Neglect	33 (52.38)	68 (43.87)
Family functioning			F = 4.031	.046	${\eta }_p^2$ = .019
Single parent	39 (61.90)	85 (54.84)	0.912	.340	.065
Exposure to DFV	36 (57.14)	79 (50.97)	0.685	.408	.056
CG substance use	33 (52.38)	76 (49.03)	0.201	.654	.030
CG Mental health	25 (39.68)	40 (25.81)	4.122	.042	.137
CG Incarceration	15 (23.81)	41 (26.45)	0.164	.686	.027
CG Inconsistency	26 (41.27)	41 (26.45)	4.620	.032	.146
CG victim of SA^1	15 (25.86)	20 (12.99)	5.067	.024	.155
Social exclusion			F = 12.286	.002	${\eta }_p^2$ = .048
Social isolation^2	38 (62.30)	58 (37.91)	10.485	.001	.221
Bullying victimisation^3	37 (60.66)	64 (42.67)	5.624	.018	.163
Poor social interaction^4	28 (45.90)	59 (38.31)	1.045	.307	.070

SSH n = 63, NSSH n = 155 except: ¹SSH n = 58, NSSH n = 154; ²SSH n = 61, NSSH n = 153; ³SSH n = 61, NSSH n = 150; ⁴SSH n = 61, NSSH n = 154.

χ²=  Pearson’s Chi-squared test; ϕ_c= Cramer’s V effect size for chi-square test; ${\eta }_p^2$ = partial eta squared effect size for F test.

Significant differences were found in family functioning-related adversities, where presence of family adversity items was greater amongst youths with sibling-directed HSBs with the exception of caregiver incarceration (although this difference was non-significant). Statistically significant differences in prevalence were demonstrated for caregiver sexual abuse victimisation and caregiver mental health problems, with youths who perpetrated sexual harm against siblings more frequently having caregivers facing these difficulties. Youths who harmed siblings were also significantly more likely to have experienced caregiver inconsistency during the first 12 years of life.

Prevalence of all domains of maltreatment were greater amongst youths with sibling HSBs. However, the MANOVA did not indicate that this difference was significant. Frequent maltreatment is a known factor contributing to a high degree of contact with child protective services, and further examination of case files reflected this, with 85.7% of youths who harmed siblings (compared to 59.35% of the non-sibling HSB cohort) having had formal contact with Child Safety services. Significant differences between groups were found in the social exclusion domain, where youths who sexually harmed siblings more frequently experienced social isolation before the age of 12, as well as bullying victimisation.

3.3. Differences in ACE scores for male youth who sexually harm siblings and nonsiblings

The number of ACEs experienced by each young person in the sample was calculated by summing ACE scores for each item to reach a total out of a possible score of 14. ACE scores for youths who harmed both siblings and non-siblings ranged from 0 to 13. As demonstrated in Figure 1, youths who sexually harmed siblings were more likely to have experienced a high number of ACEs, compared to those with non-sibling HSBs. For example, close to a third (31.1%) of youths who harmed non-siblings had few ACEs (2 or less) in their developmental histories compared to 14% of youths who harmed siblings. In contrast, almost half (49.1%) of the cohort of youths with sibling-directed HSBs had experienced 8 or more ACEs compared to a third (33.1%) of those that harmed non-siblings, and around a quarter (24.5%) of the sibling HSB cohort had experienced a very high number of ACEs (10 or more) compared to 12.2% of those that harmed non-siblings.

Figure 1. Prevalence of ACE scores for male youth who sexually harm siblings and non-siblings.

These differences in numbers of ACEs experienced were confirmed with a t-test (see Table 2) showing a significant difference in mean ACE scores for the sibling and non-sibling HSB cohorts (t(203) = 2.85, p < .01). Youths who sexually harmed siblings had experienced a greater mean number of adverse events (M = 6.75, compared to 5.21 for those with non-sibling HSBs). The effect size for this difference (d = .44) suggested a medium effect (Cohen, 1988).

Table 2. ACE scores for male youth who sexually harm siblings and non-siblings.

	Sibling sexual harm (SSH)	Non-sibling sexual harm (NSSH)	t (df)	p (2 sided)	d
Mean ACE score (SD)	6.75 (3.58)	5.21 (3.45)	2.845 (203)	.005	.444

SSH n = 57; NSSH n = 148; d = Cohen’s d measure of effect size.

3.4. Differences in psychological functioning for male youth who sexually harm siblings and non-siblings

Differences in psychological functioning and problem behaviours were assessed using chi-square tests (see Table 3). Youths who sexually harmed siblings were significantly more likely to have experienced internalising problems such as anxiety and depressed feelings during their childhoods. Significant differences were also found for early problem sexual behaviours, where these were twice as prevalent within the sibling HSB group. While differences in externalising behaviours were not found, youths with sibling victims were significantly less likely to engage in substance use.

Table 3. Psychological functioning for male youth who sexually harm siblings and non-siblings.

	Sibling sexual harm (SSH)	Non-sibling sexual harm (NSSH)	χ^2	p	ϕc
	n (%)	n (%)
Internalising problems^1	45 (75.00)	76 (51.70)	9.524	.002	.215
Externalising problems^2	38 (65.52)	100 (66.67)	0.025	.875	.011
Early problem sexual behaviours^3	23 (37.10)	28 (18.30)	8.615	.003	.200
Substance use^2	31 (53.45)	106 (70.67)	5.516	.019	.163

¹ SSH n = 60; NSSH n = 147, ²SSH n = 58; NSSH n = 150, ³SSH n = 62; NSSH n = 153.

4. Discussion

While young people who exhibit sexual harm often share common adversity-related risk factors such as maltreatment and poor family functioning, research emphasises variability within this population (Fox & DeLisi, 2018). Sexual offending by youth encompasses a broad range of offence types, victim characteristics, and modus operandi. Understanding differences in typologies of youths who sexually harm allows intervention efforts to be tailored to the specific needs of young people who have or are at risk of engaging in HSB. Greater knowledge of youths who sexually harm siblings is needed to determine how this cohort differs from other youths with HSBs.

A limited body of research has examined differences in developmental risk factors for youths who sexually harm sibling and non-siblings. Amongst those that do, some general findings commonly emerge, such as greater family dysfunction and increased likelihood of maltreatment of some kind. Studies vary however, in their findings of which specific types of abuse, neglect and poor family functioning are more (or less) prevalent amongst those with sibling-directed HSBs. There is also a lack of consensus across studies regarding differences in the psychosocial functioning of youths who sexually harm siblings compared to those with extrafamilial HSBs. The small samples utilised in many previous studies add difficulty when drawing conclusions about typological differences for youths who engage in sibling sexual harm.

4.1. Summary of findings

This study furthered understanding of the developmental characteristics of youths who sexually harm siblings. Over half of the sibling HSB cohort were found to have experienced emotional abuse (50.8%), physical abuse (57.1%), or neglect (52.38%). Over a third of the cohort (36.51%) had been sexually abused themselves. These maltreatment experiences occurred within families that most often featured single parents (61.9%), with caregivers abusing substances in half of cases (52.3%) and having been imprisoned in a quarter of cases (25.9%). Almost three in five youths who sexually harmed a sibling (57.1%) were exposed to violence within the home environment. These findings demonstrate that youths with sibling-directed HSBs predominately live in problematic and dysfunctional family environments.

Three family factors were significantly more prevalent in the backgrounds of youths who sexually harmed siblings when compared to other youths with HSBs. Firstly, caregivers of youths whot sexually harm siblings more often experienced mental health problems – around two in five (39.7%) had a formal history of mental illness (compared to 25.8% of youths with non-sibling HSBs). Secondly, a quarter of caregivers (25.9%) had experienced their own sexual abuse, which was close to double the rate amongst caregivers of youths whose sexual harm was against non-siblings (13.0%). Lastly, youths who sexually harmed siblings more often experienced inconsistency and instability in caregivers during childhood, with two in five (41.3%; compared to 26.5% of the non-sibling HSB cohort) having moved from caregiver to caregiver twice or more during the first 12 years of life (including to/from foster care).

These findings suggest who youths who sexually harm siblings live in vulnerable families where caregivers are struggling with their own traumatic experiences and psychological issues. Frequent moves during childhood might occur where caregivers are unable to effectively parent or protect children from harm. Given 85.7% of youths whose HSBs were against siblings in this study had formal contact with Child Safety services, the early instability of caregivers likely includes children being removed from the family due to abuse or neglect.

The family characteristics previously identified also affect the ability to form secure parent–child attachments. Groh et al.’s (2012) meta-analysis examining attachment and psychological functioning during childhood demonstrated that insecure attachments to primary caregivers (particularly avoidant attachment styles) were significantly associated with internalising symptomology including anxiety, social withdrawal and depression. Sibling sexual abuse may reflect situations where siblings exposed to highly dysfunctional family environments form inappropriate attachments with each other (Caffaro & Conn-Caffaro, 2005), thereby, as Caffaro (2017) explains, buffering the effect of the insecure bond to a mother and/or father.

Youths who sexually harmed siblings in this study also differed significantly from other youths with HSBs in regard to social exclusion. Poor social skills and/or rejection from similarly aged peers (62.3%), as well as victimisation through ongoing physical and/or verbal bullying at school (60.7%) was experienced by three in five youths with sibling-directed HSBs (compared to 37.9% and 42.7% respectively for those that harmed non-siblings). These findings support the hypothesis that youths unable to form appropriate peer connections may look to siblings (particularly those who are younger) to meet their needs, including sexual intimacy (Martijn et al., 2020; Worling, 2001).

While the extent of externalising behaviours was similar for youths who harmed both siblings and non-siblings (65.5% and 66.7% respectively), youths with sibling HSBs could be differentiated from other youths who sexually harm by high levels of internalising problems. Accordingly, three out of four (75.0%) youths who sexually harmed a sibling (compared to 51.7% of youths who sexually harmed non-siblings) experienced nervousness, anxiety, depressed feelings or somatic complaints such as dizziness or tiredness that impacted their functioning. They were also significantly more likely than those who sexually harmed non-siblings to have exhibited developmentally inappropriate sexual behaviours before the age of 10, including public self-stimulation and inappropriate touching of others. These behaviours may have contributed to the levels of social exclusion and bullying experienced.

In addition to greater prevalence of these specific developmental risk factors, youths who sexually harmed siblings experienced a significantly greater mean number of adverse experiences during their childhood (6.75 compared to 5.21 for those with non-sibling HSBs). Each additional childhood adversity experienced considerably increases the likelihood of future ACEs (Levenson et al., 2017). Cumulative risk literature demonstrates that where numerous risks occur, these stressors interact, with the influence of the combined risks exceeding the additive impact of each risk alone (Evans et al., 2013). This means that outcomes become much poorer as numbers of risks increase. Consequently, youths who sexually harm siblings can be seen as a very high risk group, who are facing significantly more adversities than other young people who exhibit HSBs.

With the high rates of sexual abuse amongst youths who sexually harm siblings, concomitant with caregivers having their own sexual abuse histories, it is possible that sibling-directed HSB reflects patterns of sexual dysfunction in the family unit. This could include inappropriate exposure to adult sexual activity or pornography, or greater intrafamilial offending behaviours (for example, where caregivers sexually harm children, and children sexually harm siblings).

4.2. Implications for policy and practice

This research adds to an emerging literature that demonstrates the prevalence of ACEs in the developmental histories of youths who exhibit HSBs. ACEs were found to occur more often in the lives of youths who sexually harmed siblings compared to those who sexually harmed non-siblings, making these youths particularly complex cases. These findings have important implications for treatment of youths with HSBs directed toward siblings. In many instances, youths who sexually harm siblings are both perpetrators and victims (Grant et al., 2009). This means that treatment efforts must be trauma-informed, utilising a strengths-based approach (Caffaro, 2020). The increased likelihood of problematic internalising behaviours amongst the sibling HSB cohort, which was significantly greater than for other youth with HSBs, suggests the need to address underlying psychological health issues for this cohort.

Family dysfunction, and related maltreatment, was a pertinent issue for youths who sexually harmed siblings. This highlights the need for an ecological approach to treatment, which targets the family systems within which young people exist. As noted by Caffaro and Conn-Caffaro (2005), family treatment may not always be an option, however sensitivity to problematic family relationship dynamics is necessary when providing effective therapeutic interventions (Ballantine, 2012). Family-based strategies for preventing instances of sibling sexual harm should include attention to parental monitoring and supervision to prevent opportunities for offending, but should also consider caregiver availability and attachment in instances where sibling sexual relationships reflect needs for nurturance, acceptance or validation that is not provided by a parent (Caffaro & Conn-Caffaro, 2005). The significance of family dysfunction in the histories of youths who sexually harm siblings highlights the importance of collaboration with child protection services in delivering interventions. Given youths who sexually harmed siblings were differentiated from other youths with HSBs by the extent of social isolation and rejection, attention should also be given to interventions that promote the development of interpersonal skills and social functioning, to facilitate age-appropriate peer relationships. However, research is required to determine whether such intervention can promote desistence from perpetrating sexual harm.

Findings also highlight strategies for prevention of sibling sexual abuse offences in the first instance. Youths who perpetrate sexual harm against siblings were frequently found to live in vulnerable families that come to the attention of child protection agencies. They were also noted to exhibit sexual behaviour problems prior to adolescence. This highlights possible untapped points of early intervention to prevent the onset of more serious sexual behaviour problems. Early intervention with at-risk families combined with greater awareness of characteristics of youths who go on to sexually harm siblings may help prevent emergence of these behaviours. High rates of sexual abuse victimisation within the sibling HSB cohort, as well as for caregivers of youths who sexually harm siblings, suggests the need to investigate intergenerational patterns of sexual dysfunction within families.

4.3. Limitations and future directions

Youths in this study were referred to GYFS due to perpetration of serious sexual offences and therefore represented young people with more severe HSBs and complex developmental histories. For this reason, findings may differ when considering the broader spectrum of youths who sexually harm.

While clinical case files provide a rich and unique source of information on young people receiving treatment following perpetration of sexual harm, some limitations exist. Data for this population is mostly retrospective and self-reported, although in many places supported by official documentation and other collateral information sources. We compensate for a possible bias in under or overreporting of adverse life events and/or psychological functioning by only endorsing ACEs as having been experienced where case files contain convincing evidence (and not where the specific adversity is suspected or mentioned briefly without further exploration). The nature of the sample used means that we are unable to examine resilience in the face of ACEs, and/or protective factors that aid in the prevention of youth offending amongst young people with adverse experiences.

This study was only able to examine the characteristics of male youths with HSBs due to numbers of females referred to the service being too low to draw generalisable conclusions. Further research on etiology and motivations for sexual harm (particularly against siblings) by females is needed. While most of the sample of youths with sibling HSBs were non-Indigenous, this study did not consider cultural differences in risk factors and adversities explored. This is an area requiring further research to understand the nature and extent of adversities experienced by Aboriginal and/or Torres Strait Islander young people, and the ways in which poor psychological functioning presents for this population.

Felitti et al.’s (1998) ACEs framework was used to shape the investigation of adverse experiences within this population of youths with HSBs. While this framework provides a useful starting point for understanding relationships between adversity and poor youth outcomes, it has not been developed with youth offending specifically in mind. In fact, the ACE scale was developed for a much different purpose (understanding health behaviours and outcomes of adults) and was based on a sample with very different demographic attributes to those commonly found for youths who exhibit HSBs (for example, three quarters of Felitti et al.’s (1998) sample had attended or graduated from college). In this study, the ACE framework was augmented with relevant, research-identified risk factors for young people sexually harm, as well as related variables assessing psychosocial functioning, however ideally, future research should focus on developing an ACE framework that better captures adversities relevant for this specific population.

4.4. Conclusion

As is the case with young people who exhibit HSBs in general, youths who sexually harm siblings often exist in vulnerable families, with high degrees of maltreatment. This study found that youths who perpetrated sibling-directed HSBs were differentiated from those who harmed non-siblings due to a greater prevalence of caregivers with mental health problems, who had experienced their own sexual abuse victimisation. Further, youths who sexually harmed siblings were also more likely to experience inconsistency in caregivers during their childhoods, possibly affecting attachment relationships with parents. In particular, the sibling HSB cohort was characterised by social exclusion and a high prevalence of internalising problems including anxious and depressed feelings. These findings provide further understanding of the characteristics of youths who sexually harm siblings, and are useful for guiding tailored strategies for treatment of young people with sibling-directed HSBs and prevention of sibling sexual abuse.

Acknowledgements

This research would not be possible without the work of GYFS clinicians whose clinical case files provide a unique and in-depth source of knowledge for understanding youths who exhibit HSBs. Thanks is also extended to the Department of Children, Youth Justice and Multicultural Affairs who have provided funding for the GYFS program since 2001, and to Griffith University for its in-kind support. Lastly, we extend our gratitude to the research assistants who work with GYFS.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Appendix

Original ACEs and GYFS items

Table

ACE	Original checklist item	Item in GYFS data
ACE 1	Emotional abuse Did a parent or other adult in the household often swear at you, insult you, put you down or humiliate you OR act in a way that made you afraid that you might be physically hurt	Victim of emotional maltreatment Psychological denigration and failure to provide a child with adequate emotional availability and nurturance by a person who is in a position of trust and caretaking at the time that is likely to have a negative impact on the child’s self-esteem or social competence
ACE 2	Physical abuse Did a parent or other adult in the household often push, grab, slap, or throw something at you? OR ever hit you so hard that you had marks or were injured?	Victim of physical abuse The non-accidental use of physical force against a child by a person who is in a position of trust and caretaking at the time (e.g. parent, older sibling, other relative, caregiver) and that results in harm to the child
ACE 3	Sexual abuse Did a person or adult at least 5 years older than you ever touch or fondle you or have you touch their body in a sexual way? OR try to or actually have oral, anal or vaginal sex with you?	Victim of sexual abuse Victim of hands-on sexual assault (sexual touching, sexual assault with or without violence)
ACE 4	Emotional neglect Did you often feel that no-one in your family loved you or thought you were important or special? OR your family didn’t look out for each other, feel close to each other, or support each other?	Victim of neglect Failure by parent or caregiver to provide a child (where they are in a position to do so) with the conditions that are culturally accepted as being essential for their physical and emotional development and wellbeing. As indicated in at least one of the following types of neglect: physical – failure to provide basic physical necessities such as safe, clean, and adequate clothing, housing, food and healthcare; emotional – lack of caregiver warmth, nurturance, encouragement, and support; educational – failure to provide appropriate educational opportunities for the child; environmental – failure to ensure environmental safety, opportunities and resources. Lack of involvement in child’s day to-day activities
ACE 5	Physical neglect Did you often feel that you didn’t have enough to eat, had to wear dirty clothes, and had no one to protect you OR your parents were too drunk or high to take care of you or take you to the doctor if you needed it?
ACE 6	Parental separation or divorce Were your parents ever separated or divorced?	Single-parent living environment Living in a single parent environment
ACE 7	Exposure to domestic violence Was your mother or stepmother often pushed, grabbed, slapped, or had something thrown at her? OR sometimes or often kicked, bitten, hit with a fist, or hit with something hard? OR ever repeatedly hit over at least a few minutes or threatened with a gun or knife?	Witnessing family violence Witnessing of verbal, physical or sexual violence toward another family member with whom the child has a significant relationship (including extended family and guardians). This may include direct (visual) and indirect (auditory) exposure to physical assaults on family members OR Caregiver a victim of domestic violence Caregiver has been a victim of domestic violence during the young person’s developmental years
ACE 8	Family member substance abuse Did you live with anyone who was a problem drinker or alcoholic or who used street drugs?	Caregiver substance abuse A maladaptive pattern of substance use leading to clinically significant impairment or distress. This might include being unable to fulfil major role obligations at work, school or home; absence from work; driving car while intoxicated; disorderly conduct; interpersonal problems exacerbated by effects of the substance
ACE 9	Family member mental health Was a household member depressed or mentally ill or did a household member attempt suicide?	Caregiver mental health issues Caregiver has a formal history of mental illness
ACE 10	Family incarceration Did a household member go to prison?	Family incarceration Maternal, paternal or sibling involvement in crime; criminal records; periods of incarceration; parent or stepparent or older siblings have a positive attitude towards anti-social (& criminal) behaviour; maternal, paternal or older sibling have a history of sexual offending behaviour