Comparing Solo- and Co-Offending Female Sex Offenders on Variables of Pathology,Offense Characteristics,and Recidivism

Abstract

Due to the smaller proportion of female sex offenders (2%-12% of all sexual offenses) compared with male sex offenders, we know much less about these women to aid in the assessment, treatment, and prevention of their offending behavior compared with men. One promising distinction in female sex offender typology is solo-offending females versus females who offend with a male co-offender. The current study uses a sample of 225 incarcerated female sex offenders to compare solo and co-offending women on variables of psychopathology, criminal history, victim and offender information, and recidivism rates. Results indicate that solo offenders are more likely to have male, unrelated victims, score higher on dominance and aggression, and are more likely to generally recidivate. Solo versus co-offending status was not a significant predictor for sexual recidivism. Implications for assessment and treatment are discussed.

Keywords

female sex offenders solo offenders co-offenders recidivism

Statistics released in 1993, by the National Incident-Based Reporting System (NIBRS) in the United States, indicate that only 1% of the 2,865 reported sexual offenses were committed by females (Reaves, 1993). More recent data from the United States, compiled from the Uniform Crime Report (UCR), show that for 2014, females accounted for 7% of sexual offenses (not including prostitution) and 2.8% of forcible rapes (Federal Bureau of Investigation, 2014). The National Crime Victimization survey provides higher numbers: In the 2011 report, females accounted for 18.5% (over 33,000) of the 181,830 sexual crimes involving a single offender. If the offense involved multiple victims, none out of the 13,600 cases involved exclusively females, and 24.3% involved males and females. In a recent meta-analysis of gender proportion in sexual offenders from several countries, Cortoni, Babchishin, and Rat (2017) found that 2% of sexual offenses reported to the police involved females, but females committed 12% of sexual offenses reported in victimization surveys.

These statistics and previous research have indicated that, although females sexually offend less than males, research to understand these offenders for risk assessment, effective treatment, and prevention is warranted. To date, few studies have served to inform risk assessment or to aid in the effective treatment of these offenders. Female sex offenders are assigned risk levels and placed on sex offender registries without the existence of valid assessment tools (Vess, 2011). Current literature, though limited compared with males, has provided several typologies and distinctions that are beginning to inform risk and rehabilitation for female sex offenders. One of the distinguishing differences among female sex offenders is the common occurrence of a male co-offender (Saradjian & Hanks, 1996; Williams & Bierie, 2015). Solo offenders are defined as offenders who commit the offense alone, and co-offenders are female sex offenders who commit their offenses with one or more co-offenders. This phenomenon is salient to the female sex offender: only a small percentage (approximately 12%) of male sexual offenders offend with another individual (Williams & Bierie, 2015). The authors also found that while 32.5% of the female sex offenders offended with a male co-offender, only 1.8% of the male sex offenders in their sample offended with a female co-offender (Williams & Bierie, 2015). It is logical to question whether these women are inherently different than women who offend alone and whether this distinction could serve to inform risk assessment and treatment focus for female sex offenders. Of the few studies completed, comparing female sexual offender types, findings hint that this distinction may serve to inform risk and treatment. The current study will compare psychopathology symptoms, offense characteristics, and recidivism rates of these two groups.

Typologies

One of the most researched areas of female sex offending is typology development (e.g., Mathews, Matthews, & Speltz, 1989; Mathews, Matthews, & Speltz, 1991; Nathan & Ward, 2001; Sandler & Freeman, 2007; Vandiver & Kercher, 2004). The typologies often separate samples into clusters, groups, or classes based on offense characteristics, victim characteristics, and offender characteristics. Although it is common for typologies to distinguish between female offenders who offend alone (solo offenders), or who offend with another offender (co-offenders), subsets of these groups have also been found. The solo-offender group has been commonly divided into two types: the teacher/lover group and the predisposed group (Mathews et al., 1989, 1991; Nathan & Ward, 2001). The teacher/lover group of offenders generally does not view their actions as a crime, believe that their relationship is legitimate, and any type of physical relationship is consensual. Research shows that the offender may be replacing an older adult male with a younger adolescent male, implying difficulty in forming same-age relationships with males (Mathews et al., 1991; Saradjian & Hanks, 1996). As opposed to some of the other groups in these typologies, females who offend against adolescent boys are less likely to have victimization or abuse as a child (Saradjian & Hanks, 1996). The second subset of solo offenders, the predisposed group, generally experiences psychological disorders, unhealthy relationships, and abuse as adults and children (Mathews et al., 1989, 1991). This group of women includes females who are likely to have significant histories of sexual abuse, or other severe childhood trauma, that predisposes them to engaging in sexually abusive behaviors.

Co-offenders also have two identifiable subsets. Many studies have distinguished between coerced and accompanied offenders (e.g., Mathews et al., 1991; Saradjian & Hanks, 1996). Coerced offenders are inclined to offend solely in the presence of a co-offender, may be referred to as male-coerced or simply co-offender, and have been identified in many typologies (Mathews et al., 1991; McCarty, 1986; Nathan & Ward, 2001; Saradjian & Hanks, 1996). The coerced offender reportedly has high levels of emotional dependency toward their coercer and is passive in their relationship, but active participant in the offending behavior (Gannon & Rose, 2008). Research has also shown that the coerced offenders typically victimize their own children, especially their daughters (Atkinson, 1996).

The second subset of co-offenders is the accompanied offender. Accompanied offenders are not coerced into the sexually abusive behavior, and may even initiated it themselves. This group has been identified in many typologies, and has been termed several different names, including accomplice offender (McCarty, 1986), accompanied offender (Mathews et al., 1991), co-perpetrator (Saradjian & Hanks, 1996), and willing ally (Nathan & Ward, 2001). Typologies consistently indicate distinguishable factors between offenders who offend alone or with another offender. It is reasonable to believe that this distinction may serve important in the assessment of risk, treatment need, and management of female sex offenders.

Co-Offenders Versus Solo Offenders

Researchers have indicated that there are differences between female sex offenders who are solo offenders from those who offend with a male co-offender (Budd, Bierie, & Williams, 2017; Comartin, Burgess-Proctor, Kubiak, & Kernsmith, 2018; Gillespie et al., 2015; Muskens, Bogaerts, van Casteren, & Labrijn, 2011; Vandiver, 2006; Williams & Nicholaichuk, 2001).Vandiver (2006) compared 123 female solo offenders with 104 female co-offenders and found that 68% of co-offenders offended against female victims compared with 36% of the solo offenders. Furthermore, 43% of the co-offending females offended against family members, whereas 18% of the solo offenders offended against related victims. Co-offenders were also more likely to have more than one victim (37%), contrasted with 15% of solo offenders. There were also observable differences in the type of offense committed, with more forcible sodomy (65.5% in co-offenders; 34.5% in solo offenders) and possession of pornography crimes (83% in co-offenders and 17% in solo offenders) committed by co-offenders. Co-offenders were also more likely to have more prior nonsexual offenses on record (65% of co-offenders vs. 26% of solo offenders). These were all significant differences between solo- and co-offending females. There was no significant difference between co-offenders and solo offenders on victim age at offense: the age of the victim generally fell between 12 and 17 years in both groups (Vandiver, 2006).

In a similar study, Muskens et al. (2011) compared 48 female co-offenders with 12 female solo offenders. The results reflected those of the Vandiver (2006) study, including the sex of the victim and relation of victim to offender. The authors found that 60% of solo offenders had a male victim, compared with 24% of co-offenders, and 58% of solo offenders had an unrelated victim, as opposed to 27% of co-offenders. They also found that solo offenders had a higher chance of being diagnosed with a clinical disorder, such as a mood disorder, with 89% of solo offenders receiving such a diagnosis, compared with 42% of the co-offenders (Muskens et al., 2011). These findings were significant and consistent with those of Gillespie et al. (2015) who studied a sample of 20 co-offenders and 20 solo offenders referred to the Lucy Faithfull Foundation in the United Kingdom. These authors found significantly higher levels of depression, sexual dissatisfaction, substance abuse, and mood disorders in solo offenders. Solo offenders also scored significantly higher on measures of negative mood states, abusive fantasies, and a need for power and dominance (Gillespie et al., 2015). For co-offenders, Gillespie et al. (2015) found a significantly higher number of environmental offense-preceding factors, such as having current partners who were sex offenders. Approximately 41% of co-offenders reported having dependent personalities, compared with none of the solo offenders. Antisocial behaviors were found more commonly among the co-offenders, and borderline personality disorders were found more commonly among the solo-offender groups, though the difference was not statistically significant.

In recent examinations of solo- and co-offending female sex offenders, Budd et al. (2017) and Comartin et al. (2018) compared the mental health and trauma histories, and offending patterns of these women across the types. Budd et al. (2017) used 21 years of the NIBRS data to compare different groupings of females who have sexually offended. Similar to previous research, female solo offenders were significantly more likely to have male and unrelated victims than women who offended with a male co-offender (Budd et al., 2017). The authors also reported that co-offenders were significantly more likely to have stranger victims, cause more injury, and use weapons in their sexual offense than female sex offenders who offended alone (Budd et al., 2017). Comartin et al. (2018) found, that while both childhood and adult victimization were common to solo- and co-offending females, being an adult victim of abuse was significantly more prevalent in coerced than uncoerced co-offending women.

Comparing solo- and co-offending females on general, violent, and sexual recidivism, Muskens et al. (2011) examined 60 female sex offenders with a follow-up period that averaged approximately 6 years. Results showed that one of the female sex offenders recidivated violently, and four recidivated with a general offense; none of the women in the sample sexually recidivated. Although the recidivism results are only suggestive because of the small sample size and low base rate of recidivism, Muskens et al. (2011) found that the solo offenders were significantly more likely to commit a nonsexual re-offense than the co-offenders. No other studies have compared recidivism rates and types across solo- and co-offending females.

In summary, research comparing solo to co-offending female sex offenders has recently shown distinctions between these two types. Several of these differences may serve to inform risk assessment and the rehabilitation and management of this population of offenders. Variables such as relationship to the victim, gender of the victim, number of victims, and degree of antisocial personality characteristics have all been found to significantly distinguish solo- and co-offending female sex offenders, and have been found to predict sexual recidivism for male sexual offenders (Hanson & Harris, 2000; Hanson & Thornton, 2000). For example, several of these variables are included in the most validated risk actuarial tools for male sexual offenders (Hanson & Harris, 2000; Hanson & Thornton, 2000; Harris, Rice, & Quinsey, 2003). If these factors work similarly for female sex offenders, they could help inform risk for this population of offenders. Researchers have also recently found consistent differences between solo- and co-offending female sex offenders on variables of negative mood states, need for power and dominance, injury to victim, dependency issues, history of victimization, clinical disorders, and borderline personality characteristics (Budd et al., 2017; Comartin et al., 2018; Gillespie et al., 2015; Muskens et al., 2011). If research continues to demonstrate that these variables differentiate solo from co-offending female sex offenders, they may serve to inform the treatment and management of these offenders.

The current study utilizes one of the largest samples to date to compare female sexual solo and co-offenders. It is hypothesized that female solo offenders will be more likely to offend against males and nonrelatives, to demonstrate higher levels of antisocial and borderline traits, to be more likely to report substance abuse problems, to have a higher number of previous arrests, and be more likely to recidivate than female co-offenders. It is hypothesized that female co-offenders will demonstrate higher levels of dependent personality traits and mood disorders than female solo offenders.

Method

Participants

The sample consisted of 225 women who were arrested and convicted of a sexual offense and had participated in treatment while incarcerated within the Texas Department of Criminal Justice (TDCJ) between the years of 2000 and 2013. The current sample represented 35.6% of all of the eligible females serving a prison sentence for a sexual offense during the years of file data collection (G. Engman, TDCJ, personal communication, May 22, 2017). All women participating in the treatment program were either required to participate by the parole board if they wanted to improve their chance for parole (49%), or they volunteered to attend after being asked by TDCJ officials if they had an interest in treatment (51%; G. Engman, TDCJ, personal communication September 15, 2017). The demographic information of the sample indicates that the average age and education level of the women was 31 years (SD = 8.32) and 11 years (SD = 2.40), respectively. The average IQ nonverbal estimate (Beta III; Kellogg & Morton, 1999) of the sample was 90.52 (SD = 15.28). The racial composition of the sample was predominately Caucasian (64.0%), and the remainder was Hispanic (19.1%) and African American/Black (16.9%). The marital status of the sample was 36.0% single, 34.7% married, 20.4% divorced, and 4.9% separated. The average number of previous arrests for nonsexual offenses was 1.6 (SD = 2.6) and .02 (SD = .15) for sexual offenses. The median for previous nonsexual arrests was one and the mode was zero with a range of 0 to 15, and the median and mode for prior sex offenses were both zero with a range of 0 to 1.

The majority of the sample consisted of women who had sexual offense index crimes against a child. A much smaller percentage of women (8.4%) had sexual offenses against an adult. Approximately 4.5% of the sample comprised the “Other” category that consisted of offense titles of aggravated sexual assault with a deadly weapon, injury to a child, and one compelling prostitution offense. The majority of the sample were solo offenders (60.0%), had victims who were unrelated (59.6%), and had victims who were female (54.7%). In the sample, 56.4% recidivated overall; 52.4% recidivated with a nonsexual offense and 4.0% sexually recidivated (Table 1).

Table 1.

Sample Characteristics of 225 Females Who Sexually Offended.

	n/M	%/SD
Age	30.95	8.32
Race
African American/Black	38	16.9
Hispanic	43	19.1
White	144	64.0
Marital status
Married	78	34.7
Single	81	36.0
Divorced	46	20.4
Separated	11	4.9
Other	9	4.0
Offense type
Aggravated sexual assault of child	68	30.2
Sexual assault of child	42	18.7
Indecency with a child	39	17.3
Multiple sex offense types	34	15.1
Aggravated sexual assault/sexual assault	19	8.4
Sexual performance of a child	13	5.8
Other	10	4.5
Offender type
Solo offenders	135	60.0
Co-offenders	90	40.0
Offender victimization
Offender sexually abused as child	141	65.9
Offender sexually abused as adult	32	14.9
Offender physically abused as child	105	48.8
Offender physically abused as adult	45	21.1
Victim information
Unrelated victim	134	59.6
Female victim	123	54.7
Previous arrests	1.6	2.6
Recidivism rates
Overall	127	56.4
Nonsexual	118	52.4
Sexual	9	4.0

Measures

The Personality Assessment Inventory (PAI)

The PAI (Morey, 1991) is a self-administered 344-item assessment tool that is utilized to evaluate psychological and personality functioning. Each item in the assessment can be answered with totally false, slightly true, mainly true, and very true; this allows the PAI to assess the intensity of the feature in each item (Morey, 1996). The PAI utilizes 22 nonoverlapping full scales, including four validity, 11 clinical, five treatment consideration, and two interpersonal scales (Morey, 1996). According to research completed by Morey (1991), the PAI has shown high levels of validity across samples of clinical patients, college students, and the general population, each with sample sizes greater than 1,000 individuals. Research analyzing the validity of the PAI in samples of general offenders and sexual offenders has shown that the PAI is an accurate measure for antisocial disorders, and personality disorders in a forensic setting (Morey & Quigley, 2002). In addition, Boccaccini, Rufino, Jackson, and Murrie (2013) found that the PAI was a useful assessment for risk level of misconduct involving female sex offenders during treatment.

Recidivism

Recidivism, defined as any arrest postprison release for the offender’s index sexual offense, was split into sexual and nonsexual types. Nonsexual offenses were any re-arrest that was not a sexual offense, such as arrests for theft, drug possession, and assault. Sexual recidivism offenses included any arrest for sexual assault of an adult or child, such as indecency with a child, sexual assault of a child, sexual assault, aggravated sexual assault, and sexual performance of a child. Pseudorecidivism was ruled out by examination of the dates of offense, arrest, and sentencing for each of the sexual recidivists to confirm that the sexual re-offense occurred after the index sexual offense. Prostitution, or failure to register as a sex offender, was not included as sexual recidivism and were coded as nonsexual offenses.

Recidivism data on each offender was collected from the Texas Department of Public Safety’s criminal database website. The DPS data included offense, arrest, and sentencing dates for the sample. The average follow-up time (time at risk) for the entire sample was approximately 5 years (M = 5.11; SD = 3.69), and spanned from the year 2002 to when recidivism data were collected in the beginning of 2014. The average time to recidivate for the women who committed another offense was 2.5 years, with follow-up time ranging from 1 to 12 years. The average time to recidivism, and the average follow-up time for nonrecidivists, were calculated by comparing the date of recidivism, or date of recidivism data collected (for nonrecidivists), to the completion date of the prison release paperwork finalized by a TDCJ professional at the offender’s time of release.

Procedure

The study was approved by the Sam Houston State University research review board and the TDCJ institutional research review board. Demographic, offense, victim information, history of victimization, and psychopathology testing data were collected from the files located in the treatment unit within the TDCJ. The sample included all women who participated in the female sex offender treatment program in the TDCJ between 2000 and 2013. The recidivism and arrest data were collected by accessing the Department of Public Safety’s criminal history website. All of the data were recorded with code sheets utilized to standardize the collection of variables.

Overview of Analyses

For the victim gender, victim relation, previous arrest, offender victimization, and recidivism analyses, a two-step approach was instituted. First, chi-squared analyses were run to assess whether there were any significant differences between solo and co-offenders. Following the chi-squared analyses, Cohen’s d was calculated using a formula provided by Sánchez-Meca, Chacón-Moscoso, and Marín-Martínez (2003). This formula uses an odds ratio generated from the 2 × 2 contingency table to calculate Cohen’s d and is provided below:

d = \frac{1}{1.65} [\ln (\frac{{b + . 5} {c + . 5}}{{a + . 5} {d + . 5}})] .

In addition, Sánchez-Meca and colleagues (2003) provided a formula for calculating the variance for Cohen’s d, which is

Variance of d = . 3675 (\frac{1}{a + . 5} + \frac{1}{b + . 5} + \frac{1}{c + . 5} + \frac{1}{d + . 5}) .

The direction of the analysis, for interpretive purposes, was designed so positive effect size values indicate the effect of solo-offender status, whereas negative values indicate the effect of co-offender status. For the analysis of victim age and scores on the PAI, a separate two-step process was utilized. First, independent sample t tests were performed to assess if any significant differences in PAI scores existed between co-offenders and solo offenders. Second, Cohen’s d was calculated for each scale of the PAI. The direction of the analysis for PAI scores is identical to the dichotomous analyses, with positive values indicating the effect of solo-offender status and negative values indicating the effect of co-offender status. The interpretation of effect size used for the current study was derived from Cohen (1988), and in this interpretation, an effect size of at least 0.2 indicates a small effect, 0.5 indicates a moderate effect, and 0.8 indicates a large effect. In addition, when effect size with 95% confidence intervals do not include 0.00, they can be interpreted as significant.

It should be noted that there were PAI data missing for some of the female sexual offenders in the sample. The missing data resulted in 16 solo offenders and seven co-offenders being excluded from the analysis. To determine whether these data were missing at random or systematically, missing data analyses were run in SPSS. No missing data patterns were found in cases that were missing PAI scores and results of Little’s MCAR (missing completely at random) test was nonsignificant, indicating that the data were missing at random.

Results

Psychopathology and Personality

Cohen’s effect sizes and t tests were utilized to examine the hypotheses that female sex offenders, who offend with a co-offender, will score higher on measures of dependent personality characteristics and mood disorders, and solo offenders will score higher on measures of antisocial disorders, borderline personality, and substance abuse (Table 2). The analyses indicate that solo offenders scored significantly higher on measures of aggression, dominance, and warmth, whereas co-offenders scored significantly higher on anxiety and anxiety-related disorders. The Cohen’s d values indicate small to moderate effect sizes.

Table 2.

PAI Score Means for Solo Offenders and Co-Offenders (n = 202).

	Solo offenders^a		Co-offenders^b				95% CI for Cohen’s d
	M	SD	M	SD	t (200)	Cohen’s d	Lower	Upper
AGG	56.49	13.82	51.17	12.99	2.75**	0.39	0.11	0.68
ALC	59.54	17.116	56.88	17.03	1.08	0.16	−0.13	0.44
ANT	61.01	12.31	57.81	10.90	1.90	0.26	−0.02	0.54
ANX	60.19	13.77	64.33	13.84	−2.09*	−0.30	−0.58	−0.02
ARD	63.21	13.84	67.36	11.98	−2.21*	−0.32	−0.60	−0.03
BOR	66.43	13.03	66.60	12.48	−0.09	−0.01	−0.29	0.27
DEP	61.69	14.89	64.77	15.30	−1.43	−0.21	−0.49	0.07
DOM	48.66	12.28	43.65	12.81	2.79**	0.41	0.12	0.69
DRG	67.09	18.59	63.86	17.53	1.24	0.17	−0.11	0.45
WRM	46.93	10.53	43.63	12.15	2.05*	0.31	0.03	0.59

Note. AGG = aggression; ALC = alcohol problems; ANT = antisocial features; ANX = anxiety; ARD = anxiety-related disorder; BOR = borderline features; DEP = depression; DOM = dominance; DRG = drug problems; WRM = warmth.

n = 119.

n = 83.

p < .05. **p < .01.

Although not statistically significant determined by the t test result, small effects were found on the scores of antisocial personality features and depressive symptoms on the Cohen’s d values. Solo-offending females had higher scores of antisocial personality symptoms and co-offending females had higher scores on depressive symptoms. Both of these findings are interpreted with caution.

History of Victimization

Offender trauma history was compared between solo offenders and co-offenders using a chi-squared analysis and Cohen’s effect sizes (Table 3). Results indicate that there is no effect for physical abuse as a child, small effects for physical abuse as an adult and sexual abuse as a child, and a moderate effect for sexual abuse as an adult. These analyses suggest that co-offending female sexual offenders are more likely to experience physical or sexual abuse, at any point in their lives, when compared with solo offenders, and this relationship is the largest for sexual abuse experienced as an adult. Confidence intervals for Cohen’s effect sizes are provided in Table 3.

Table 3.

Cross-Tabulations of Offender Victimization History.

	Offender sexually abused as child		χ² (df)	p	Cohen’s d	95% CI for Cohen’s d
	No (%)	Yes (%)	χ² (df)	p	Cohen’s d	Lower	Upper
Solo offenders	48 (38.1)	78 (61.9)	2.16 (1)	.14	0.26	−0.09	0.62
Co-offenders	25 (28.4)	63 (71.6)
	Offender sexually abused as adult		χ² (df)	p	Cohen’s d	95% CI for Cohen’s d
	No (%)	Yes (%)	χ² (df)	p	Cohen’s d	Lower	Upper
Solo offenders	116 (91.3)	11 (8.7)	9.48 (1)	<.01	0.71	0.23	1.18
Co-offenders	67 (76.1)	21 (23.9)
	Offender physically abused as child		χ² (df)	p	Cohen’s d	95% CI for Cohen’s d
	No (%)	Yes (%)	χ² (df)	p	Cohen’s d	Lower	Upper
Solo offenders	67 (52.8)	60 (47.2)	0.32 (1)	.58	0.09	−0.24	0.43
Co-offenders	43 (48.9)	45 (51.1)
	Offender physically abused as adult		χ² (df)	p	Cohen’s d	95% CI for Cohen’s d
	No (%)	Yes (%)	χ² (df)	p	Cohen’s d	Lower	Upper
Solo offenders	103 (82.4)	22 (17.6)	2.26 (1)	.13	0.30	−0.10	0.71
Co-offenders	65 (73.9)	23 (26.1)

Note. n = 214 to 215 depending on missing data.

Victim Characteristics

The next analyses involved comparing solo and co-offenders on victim characteristics. Results of the chi-squared analysis and Cohen’s effect size for victim gender and relation, as well as the results of the t test for victim age, can be found in Table 4. In line with the hypotheses made regarding victim characteristics, solo offenders were significantly more likely to have nonrelated victims than the co-offending female sex offenders and co-offenders were significantly more likely to have female victims than solo offenders. There were no significant differences between the offender types on victim age. Cohen’s d values indicate large effect sizes.

Table 4.

Cross-Tabulations of Victim Gender, Relationship, and Age.

	Gender		χ² (df)	p	Cohen’s d	95% CI for Cohen’s d
	Female victim (%)	Male victim (%)	χ² (df)	p	Cohen’s d	Lower	Upper
Solo offender	52 (40.0)	78 (60.0)	38.910 (1)	<.01	−1.17	−1.57	−0.78
Co-offender	71 (82.6)	15 (17.4)
	Relation		χ² (df)	p	Cohen’s d	95% CI for Cohen’s d
	Nonrelative (%)	Relative (%)	χ² (df)	p	Cohen’s d	Lower	Upper
Solo offender	100 (75.2)	33 (24.8)	35.901 (1)	<.01	1.03	0.68	1.39
Co-offender	31 (34.8)	58 (65.2)
	Solo offender	Co-offender	t(df)	p	Cohen’s d	95% CI for Cohen’s d
	M (SD)	M (SD)	t(df)	p	Cohen’s d	Lower	Upper
Victim age	11.96 (4.69)	11.21 (4.46)	1.20 (223)	.23	0.16	−0.10	0.43

Note. n = 216 to 225 depending on missing data.

Criminal History and Recidivism

For the hypothesis predicting that female sexual offenders who offend alone would have more previous arrests, chi-squared analyses and Cohen’s effect sizes were used (Table 5). There were no significant differences between solo and co-offenders on prior criminal history.

Table 5.

Cross-Tabulations of Previous General, Violent, and Sexual Arrests (n = 225).

	Previous nonsexual arrests		χ² (df)	p	Cohen’s d	95% CI for Cohen’s d
	None (%)	One or more (%)	χ² (df)	p	Cohen’s d	Lower	Upper
Solo offenders	65 (48.1)	70 (51.9)	.359 (1)	.55	−0.10	−0.43	0.23
Co-offenders	47 (52.2)	43 (47.8)
	Previous sexual arrests		χ² (df)	p	Cohen’s d	95% CI for Cohen’s d
W	None (%)	One or more (%)	χ² (df)	p	Cohen’s d	Lower	Upper
Solo offenders	132 (97.8)	3 (2.2)	0.000 (1)	1.00	0.04	−0.98	1.06
Co-offenders	88 (97.8)	2 (2.2)

The final hypothesis, that solo offenders would be more likely to recidivate, was tested using two chi-squared analyses and Cohen’s effect sizes (Table 6). The overall recidivism rates for the sample were 52.4% (n = 118) for nonsexual recidivism and 4.0% (n = 9) for sexual recidivism. Results indicated a moderate effect for nonsexual recidivism (d = −0.64) and the 95% CIs indicated this effect was significant. As shown in Table 6, significantly more solo offenders re-offended with general or violent offenses (nonsexual) than the co-offending female sex offenders.

Table 6.

Cross-Tabulations of Nonsexual and Sexual Recidivism (n = 224).

	Nonsexual recidivism		χ² (df)	p	Cohen’s d	95% CI for Cohen’s d
	No (%)	Yes (%)	χ² (df)	p	Cohen’s d	Lower	Upper
Solo offenders	50 (37.3)	84 (62.7)	14.61 (1)	<.01	−0.64	−0.97	−0.31
Co-offenders	57 (63.3)	33 (36.7)
	Sexual recidivism		χ² (df)	p	Cohen’s d	95% CI for Cohen’s d
	No (%)	Yes (%)	χ² (df)	p	Cohen’s d	Lower	Upper
Solo offenders	130 (97.0)	4 (3.0)	0.92 (1)	.33	0.37	−0.09	0.83
Co-offenders	85 (94.4)	5 (5.6)

The solo and co-offending women did not significantly differ in their rate of sexual recidivism. Of the four solo offenders who recidivated sexually, their re-offenses included sexual assault of a child, sexual performance of a child, indecency with a child, and indecency with a child by contact. Of the five co-offending females who sexually recidivated, their re-offenses included two indecency with a child by contact, two aggravated sexual assault, and one sexual assault.

Discussion

Research examining risk assessment and treatment targets for males who have sexually offended is rich and informative. Evaluators and treatment providers working with females who have sexually offended have few informative research results to guide their practice. In fact, females who are assigned risk levels for the public sex offender registry, or for supervision and treatment purposes, have not been given this risk level by any validated measures or procedures (Vess, 2011). In addition, treatment providers working with females are left wondering which criminogenic factors are important for rehabilitative focus. As research examining females who have sexually offended begins to increase, a promising distinction for assessment and information for treatment focus is the comparison between females who sexually offend alone compared with females who sexually offend with a male co-offender (Budd et al., 2017; Comartin et al., 2018; Gillespie et al., 2015; Muskens et al., 2011). Using one of largest samples of females who have sexually offended, the current study sought to compare solo and co-offending females on variables of psychopathology, offending characteristics, and recidivism. It was hypothesized that solo offenders would be more likely to offend against males who were nonrelatives, report higher levels of antisocial and borderline personality traits, be more likely to report substance abuse, have a great number of prior arrests, and be more likely to recidivate than females who sexually offend with a male co-offender. It was also hypothesized that co-offending females would demonstrate higher levels of dependent personality and mood disorder symptoms than solo-offending females. Results of the current study support the majority of the hypotheses.

Psychopathology and Personality

Significant differences between solo- and co-offending female sex offenders were found on scores of aggression, dominance, comfort in relationships (warmth), anxiety, and anxiety-related disorders. Small-to-moderate effects were found for solo offenders having higher scores on aggression, dominance, and comfort in relationships (warmth), whereas small-to-moderate effects were found for co-offenders having higher scores on anxiety and anxiety-related disorders. In addition, two psychopathology scales were found to have small effect sizes according to the Cohen’s d statistic: depression and antisocial personality symptoms. Although these last two results warrant further validation, they suggest that solo offenders report higher levels of antisocial personality traits and co-offending females report more symptoms of depression. Previous research has found similar significant relationships between personality and pathology characteristics across female sex offender types. For example, Gillespie et al. (2015) and Muskens et al. (2011) reported that solo sex-offending females scored significantly higher on measures of aggression and need for dominance, depression, substance abuse, and were more likely to be diagnosed with a clinical disorder, compared with co-offending females. Further research on differing pathology symptoms across solo and co-offending females is warranted before any specific symptomatology treatment focus is suggested according to offender type. In fact, several authors have suggested that female sexual offenders, overall, have higher rates of psychopathology, relationship issues, and victimization histories (Comartin et al., 2018; Johansson-Love & Fremouw, 2006; Miccio-Fonseca, 2000; Miller, Turner, & Henderson, 2009) that warrant treatment attention compared with their male counterparts.

The findings of this study also reflected the findings of Gillespie et al. (2015) in that no significant differences were found between solo offenders and co-offenders on measures of substance and alcohol abuse. This finding does not indicate that females who sexually offend do not have problems with substance or alcohol abuse. In fact, many of the females in the current sample scored in the clinical range of the PAI for problems resulting from drug use. This finding is consistent with the results of two latent profile analysis studies that found specific groupings of females who sexually offend with drug and alcohol problems (Miller et al., 2009; Turner, Miller, & Henderson, 2008) and other authors reporting common substance abuse problems among female sexual offenders (Comartin et al., 2018; Sandler & Freeman, 2009). These consistent results suggest that substance abuse may be an important factor for treatment and prevention for females who sexually offend.

History of Victimization

Prior studies have indicated that females who sexually offend are likely to have personal histories of victimization and higher rates of victimization than general justice-involved females (Christopher, Lutz-Zois, & Reinhardt, 2007; Miccio-Fonseca, 2000; Strickland, 2008). The current results support these previous findings, with over half of the sample reporting histories of childhood sexual and physical abuse and 15% to 20% reporting being a victim of adult sexual or physical abuse. Comparing solo- to co-offending females, the current study found that co-offending female sexual offenders are more likely to experience physical or sexual abuse as a child and as an adult when compared with solo offenders. The strongest prior victimization relationship between solo- and co-offending females was found for sexual abuse experienced as an adult; co-offending women were significantly more likely to experience sexual abuse in their adulthoods than solo offenders. This result is similar to the findings reported by Comartin et al. (2018), where co-offending females in their sample reported significantly higher adult victimization at the hands of their male partner. These consistent results further highlight the importance of assessing the possibility of past victimization for treatment purposes when working with females who have sexually offended, especially with those women who had male co-offenders.

Victim Characteristics

In the current study, approximately 40% of the women sampled had related victims, and about half of the sample victimized females. These findings are consistent with prior research that found that females who sexually offend are more likely to sexually offend against related victims and to have same sex victims compared with their male counterparts (Gannon & Cortoni, 2010). Comparing solo- and co-offending females, the current study found that solo female offenders were significantly more likely to offend against males who were unrelated. Other researchers (Budd et al., 2017; Muskens et al., 2011; Vandiver, 2006) have supported this finding, indicating a consistent difference in victim characteristics between solo- and co-offending females. As the majority of female sex offenders are heterosexual, it appears that solo offenders are more likely to follow their own sexual orientation, whereas co-offending females are more likely to follow (or be coerced to follow) their male co-offender’s sexual orientation. This distinction further supports the possibility of differing contributing factors to sex offending, and possible treatment needs, between co-offending and solo-offending females and between female and male sexual offenders in general.

Criminal History and Recidivism

The analyses assessing the criminal history risk variables indicated that there was no relationship between female sex offender type and prior sexual offending history. In contrast, solo-offending females had a higher rate of prior nonsexual arrests compared with co-offending females, however, this effect was small (d = .10) and not statistically significant. This tentative finding, along with the above-stated results that solo-offending women score significantly higher on aggression and dominance than the female co-offenders, indicate the possibility that female solo offenders may sexually offend as a result of an overall antisocial lifestyle rather than potential deviant sexual interest. In fact, researchers have suggested that most females who sexually offend are more similar to general justice-involved women than they are to males who sexually offend (Sandler & Freeman, 2009). These results suggest that treatment for females who sexually offend may be more effective in reducing overall recidivism if general criminogenic factors are considered in addition to possible deviant sexual interest.

The recidivism rates in the current sample are similar to previous findings: moderate/high rates of general, or non-sexual, recidivism and low rates of sexual recidivism. Of the 225 females included in the study, nine (4.0%) and 118 (52.4%) were sexually and nonsexually recidivated, respectively. Most of the nonsexual re-offenses were drug or property offenses, or a failure to comply with parole rules. These recidivism results, the criminal history findings reported above, as well as previous recidivism studies with female sex offenders (e.g., Sandler & Freeman, 2009), further suggest that the majority of females who sexually offend are not specialists in sexual offending, but their sex offending may be more likely an outcome from a general antisocial lifestyle. These women seem to be more similar to general justice-involved females than male sexual offenders.

Comparing nonsexual recidivism rates across female offender type, the solo-offending females were more likely to recidivate than the co-offending females. The area under the curve estimate indicated that solo offender status predicted nonsexual recidivism significantly better than chance. Offender type did not predict sexual recidivism, although the proportion of co-offending females recidivating with a sexual offense was higher than the solo offenders (5.6% vs. 3%): Of the nine sexual recidivists, five were co-offending and four were solo-offending females. All four of the sexually recidivating solo-offending females re-offended against a child. Two of the five co-offenders who recidivated sexually offended against children and three sexually offended against adults. This finding is unique to this study and requires further replication, but suggests that the co-offending females were likely to again be influenced by a male co-offender upon release from prison; typically women who offend against other adults do so with male co-offenders (Budd et al., 2017).

Limitations

Limitations of the current study include the sample composition and recidivism base rates. The sample utilized for this study represented a prison population, while the majority of females who sexually offend are more likely to serve probated sentences (Sandler & Freeman, 2011; TDCJ, 2014; Vandiver, Dial, & Worley, 2008). In addition, this sample of offenders participated in an 18-month, cognitive/behavioral sex offender treatment program, represented approximately 36% of the females serving prison sentences for sexual offenses within the TDCJ, and consisted of both women required to participate and program volunteers, which further affects the generalizability of the findings. As not all females who have sexually offended receive treatment in prison, the women in the current sample may have a reduced likelihood of recidivism compared with untreated women. Further research examining risk and recidivism with females who have sexually offended should include samples of women who do and do not receive treatment.

Although the current study included a larger sample of females who have sexually offended than most previous studies, the sample size remains small for statistical confidence in the findings related to sexual recidivism. Similar to all prior studies of females who sexually offend, the current study found few sexual recidivists. While this is a good finding overall, and further validates that female sex offenders have very low rates of sexual recidivism, the small number of sexual recidivists makes it statistically difficult, if not impossible, to effectively test for possible risk variables for these offenders. Large samples of females who sexually offend are required to establish valid predictors of sexual recidivism. However, it is not likely that any risk assessment tool would more accurately estimate risk of recidivism in women than simple reliance on base rates given that sexual re-offense among females is a highly unlikely event.

Conclusion

Females who sexually offend are one of the most underresearched groups of offenders in criminal justice. Although previous literature on these women has provided findings on basic demographic information and various typologies, few of these findings have informed prevention, treatment, or risk assessment. However, professionals within the criminal justice system in Texas, and several other jurisdictions in the United States and abroad, are legislatively required to assign risk levels to these women when placed on the sexual offender registry and to successfully manage and treat these offenders to reduce the likelihood of sexual recidivism. The current study, using one of the largest samples of females who have sexually offended to date, provides further validation of the overall characteristics of females who sexually offend, as well as the consistent differences between solo- and co-offending women. The results suggest that female solo offenders may be at higher risk of further general offenses and have different treatment needs than co-offending female sex offenders.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

References

Atkinson

J. L.

(1996). Female sex offenders: A literature review. Forum, 8, 39-42.

Boccaccini

M. T.

Rufino

K. A.

Jackson

R. L.

Murrie

D. C.

(2013). Personality Assessment Inventory scores as predictors of misconduct among sex offenders civilly committed as sexually violent predators. Psychological Assessment, 25, 1390-1395. doi:10.1037/a0034048

Budd

K. M.

Bierie

D. M.

Williams

(2017). Deconstructing incidents of female perpetrated sex crimes: Comparing female sexual offender groupings. Sexual Abuse: A Journal of Research and Treatment, 29, 267-290. doi:10.1177/1079063215594376

Christopher

Lutz-Zois

C. J.

Reinhardt

A. R.

(2007). Female sexual offenders: Personality pathology as a mediator of the relationship between childhood sexual abuse history and sexual abuse perpetration against others. Child Abuse & Neglect, 31, 871-883.

Cohen

(1988). Statistical power analysis for the behavioral sciences. Hillsdale, NJ: Lawrence Erlbaum.

Comartin

E. B.

Burgess-Proctor

Kubiak

Kernsmith

(2018). Factors related to co-offending and coerced offending among female sex offenders: The role of childhood and adult trauma histories. Violence and Victims, 33, 53-74.

Cortoni

Babchishin

K. M.

Rat

(2017). The proportion of sexual offenders who are female is higher than thought: A meta-analysis. Criminal Justice and Behavior, 44, 145-162. doi:10.1177/0093854816658923

Federal Bureau of Investigation. (2014). Crime in the United States 2013. Washington, DC: U.S. Department of Justice. Retrieved from https://ucr.fbi.gov/crime-in-the-u.s/2013/

Gannon

T. A.

Cortoni

(2010). Females who sexually offend: Theory, assessment and treatment. West Sussex, UK: Wiley-Blackwell.

10.

Gannon

T. A.

Rose

M. R.

(2008). Female child sexual offenders: Towards integrating theory and practice. Aggression and Violent Behavior, 13, 442-461. doi:10.1016/j.avb.2008.07.002

11.

Gillespie

S. M.

Williams

Elliott

I. A.

Eldridge

H. J.

Ashfield

Beech

A. R.

(2015). Characteristics of females who sexually offend: A comparison of solo and co-offenders. Sexual Abuse: A Journal of Research and Treatment, 27, 284-381. doi:10.1177/1079063214556358

12.

Hanson

R. K.

Harris

(2000). The Sex Offender Needs Assessment Rating (SONAR): A method for measuring change in risk levels. Retrieved from https://www.publicsafety.gc.ca/cnt/rsrcs/pblctns/sx-ffndr-nd/index-en.aspx

13.

Hanson

R. K.

Thornton

(2000). Improving risk assessments for sex offenders: A comparison of three actuarial scales. Law and Human Behavior, 24, 119-136.

14.

Harris

Rice

M. E.

Quinsey

V. L.

(2003). A multisite comparison of actuarial risk instruments for sex offenders. Psychological Assessment, 15, 413-425. doi:10.1037/1040-3590.15.3413

15.

Johansson-Love

Fremouw

(2006). A critique of the female sexual perpetrator research. Aggression and Violent Behavior, 11, 12-26.

16.

Kellogg

C. E.

Morton

N. W.

(1999). Beta-Third Edition (Beta-III). San Antonio, TX: Pearson.

17.

Mathews

Matthews

J. K.

Speltz

(1989). Females who sexually offend. Brandon, VT: The Safer Society.

18.

Mathews

Matthews

J. K.

Speltz

(1991). Females who sexually offend: A typology. In Patton

(Ed.), Family sexual abuse: Frontline research and evaluation (pp. 199-219). Newbury Park, CA: Sage.

19.

McCarty

L. M.

(1986). Mother-child incest: Characteristics of the offender. Child Welfare, 65, 447-458.

20.

Miccio-Fonseca

L. C.

(2000). Adult and adolescent female sex offenders: Experiences compared to other female and male sex offenders. Journal of Psychology & Human Sexuality, 11, 75-88.

21.

Miller

H. A.

Turner

Henderson

C. E.

(2009). Psychopathology of sex offenders: A comparison of males and females using latent profile analysis. Criminal Justice and Behavior, 36, 778-792. doi:10.1177/0093854809336400

22.

Morey

L. C.

(1991). Personality Assessment Inventory professional manual. Odessa, FL: Psychological Assessment Resources.

23.

Morey

L. C.

(1996). An interpretive guide to the Personality Assessment Inventory (PAI). Odessa, FL: Psychological Assessment Resources.

24.

Morey

L. C.

Quigley

B. D.

(2002). The use of the Personality Assessment Inventory (PAI) in assessing offenders. International Journal of Offender Therapy and Comparative Criminology, 46, 333-349. Retrieved from https://journals-sagepub-com.web.bisu.edu.cn/home/ijo

25.

Muskens

Bogaerts

van Casteren

Labrijn

(2011). Adult female sexual offending: A comparison between co-offenders and solo offenders in a Dutch sample. Journal of Sexual Aggression, 17, 46-60. doi:10.1080/1355600.2010.544414

26.

Nathan

Ward

(2001). Females who sexually abuse children: Assessment and treatment issues. Psychiatry, Psychology and Law, 8, 44-55. Retrieved from http://www.tandfonline.com/toc/tppl20/current

27.

Reaves

B. A.

(1993). Using NIBRS data to analyze violent crime (Bureau of Justice Statistics Technical Report). Washington, DC: U.S. Department of Justice, Office of the Justice Programs, Bureau of Justice Statistics. Retrieved from https://www.bjs.gov/content/pub/pdf/unibrsdavc.pdf

28.

Sánchez-Meca

Chacón-Moscoso

Marín-Martínez

(2003). Effect-size indices for dichotomized outcomes in meta-analysis. Psychological Methods, 8, 448-467. doi:10.1037/1082-989X.8.4.448

29.

Sandler

J. C.

Freeman

N. J.

(2007). Typology of females who sexually offend: A test of Vandiver and Kercher. Sexual Abuse: Journal of Research and Treatment, 19, 73-89. doi:10.1007/s11194-007-9037-4

30.

Sandler

J. C.

Freeman

N. J.

(2009). Female sex offender recidivism: A large-scale empirical analysis. Sexual Abuse: A Journal of Research and Treatment, 21, 455-473. doi:10.1177/1079063209347898

31.

Sandler

J. C.

Freeman

N. J.

(2011). Female sex offenders in the criminal justice system: A comparison of arrests and outcomes. Journal of Sexual Aggression, 17, 61-76.

32.

Saradjian

Hanks

(1996). Women who sexually abuse children. Chichester, UK: John Wiley.

33.

Strickland

S. M.

(2008). Female sex offenders: Exploring personality, trauma, and cognitive distortions. Journal of Interpersonal Violence, 23, 474-489.

34.

Texas Department of Criminal Justice. (2014). Statistical report: Fiscal year of 2014. Retrieved from https://www.tdcj.state.tx.us/documents/Statistical_Report_FY2014.pdf

35.

Turner

Miller

H. A.

Henderson

C. E.

(2008). Latent profile analyses of offense and personality characteristics in a sample of incarcerated females who sexually offend. Criminal Justice and Behavior, 35, 879-894. doi:10.1177/0093854808318922

36.

Vandiver

D. M.

(2006). Females who sexually offend: A comparison of solo offenders and co-offenders. Violence and Victims, 21, 339-354. Retrieved from http://www.springerpub.com/violence-and-victims.html

37.

Vandiver

D. M.

Dial

K. C.

Worley

R. M.

(2008). A qualitative assessment of registered female sex offenders: Judicial processing, experiences and perceived effects of the public registry. Criminal Justice Review, 33, 177-198.

38.

Vandiver

D. M.

Kercher

(2004). Offender and victim characteristics of registered females who sexually offend in Texas: A proposed typology of female sexual offenders. Sexual Abuse: A Journal of Research and Treatment, 16, 121-137. doi:1079-0632/04/0400-0121/0

39.

Vess

(2011). Risk assessment with female sex offenders: Can women meet the criteria of community protection laws? Journal of Sexual Aggression, 17, 77-91.

40.

Williams

K. S.

Bierie

D. M.

(2015). An incident-based comparison of female and male sexual offenders. Sexual Abuse: A Journal of Research & Treatment, 27, 235-257. doi:10.1177/107906324544333

41.

Williams

S. M.

Nicholaichuk

(2001, October). Assessing static risk factors in adult female sex offenders under federal jurisdiction in Canada. Paper presented at the 20th Annual Research and Treatment Conference of the Association for the Treatment of Sexual Abusers, San Antonio, TX.