Caso 1: Modelo basado en Rampas de Potencia

A large number o f research studies have attempted to establish whether a childhood experience o f sexual abuse is a risk factor for subsequent abusive behaviour. Before their results are described and any conclusions drawn, however, some o f the methodological weaknesses that can be found in this literature will be highlighted. There are three main issues to be outlined. These relate to the inappropriateness o f the research designs employed, inconsistencies with sample selection and the reliability o f self-report measures.

3,2,1 Methodological issues

The vast majority o f studies that have attempted to provide evidence that childhood sexual victimisation is a risk fector for sexually perpetrating behaviour have employed retrospective designs (e.g. Craissati & McClurg, 1996; James & Neil, 1996). That is, they involved finding out from a group o f individuals, identified in adolescence or adulthood

as sex offenders, the proportion who had been sexually victimised in childhood. The problems with this approach when attempting to identify risk factors have been described above (see Section 3.1).

There have also been problems with the sampling in studies that have investigated the role o f childhood sexual victimisation in the development o f sexually abusive behaviour. There seems to have been little consistency in the types o f offenders and comparison groups employed in these studies. The samples were often drawn firom populations of either child sex offenders (e.g. Freund & Kuban, 1994), rapists (e.g. Haapasalo & Kankkonen, 1997), or some mixture o f the two (e.g. Awad & Saunders, 1991). Some of them investigated several different groups of offenders and non-offenders (e.g. Craissati & McClurg, 1996), whilst many merely asked one group o f sex offenders, failing to draw any comparisons with a non sex-offending group (Epps, 1991; Richardson, Graham, Bhate & KeUy, 1995). Others still mixed males and females to form a single study group (James & Neil, 1996).

It is therefore difficult to establish a consistent answer as to whether childhood sexual victimisation is a risk factor for sexually abusive behaviour, since this outcome is defined so inconsistently. In addition, the use o f mixed samples (e.g. both genders, different types o f sex offenders) makes a valid interpretation even more difficult, as sexual victimisation may represent a risk factor for males but not for females, or for child abusers but not rapists.

A further problem lies m the fact that the subjects in these studies, as perpetrators of sexual abuse, would have a vested interest in stating that they were once victims o f abuse. There is quite simply a possibility that they might not be telling the truth, either consciously or not, in order to provide a convenient explanation for why they themselves have perpetrated abuse. Whatever the reason is, the result would be an inaccurate estimate o f the proportion o f abusers who were abused. The association o f childhood victimisation to subsequent offending might therefore be exaggerated.

Indeed, there is some evidence that this over-reporting o f abuse has occurred (Hindman, 1988). In her clinic for adult child molesters in Oregon, USA, Hindman would ask the men for a detailed sexual history as an initial part o f their treatment. This included questions about whether they had been child victims o f sexual abuse themselves. In the first two years this was done, the proportion o f sex offenders who reported previous sexual victimisation was found to be 67% (N = 40). Form this point onwards, all new sex offenders at the clinic were informed that they would also have to undergo a polygraph test to establish the veracity o f their claims. If they failed the test, they were told they would go back to prison. Over the foUowing six years the proportion claiming sexual victimisation suddenly dropped to 29%.

The post polygraph group represented an entirely different sample o f offenders to the previous years, and it is possible that the drop could be explained by this fact. However, such an e?q)lanation would represent a remarkable coincidence. The results do, at the very least, suggest that the reported proportions o f abused sex offenders obtained fi*om cross sectional studies might be over-estimates.

3,2.2 Prevalence o f child sexual abuse amongst adult sexual offenders

Bearing these three issues in mind, the foUowing section represents the findings fix)m a range o f studies looking at the proportions o f sex offenders Wio had been sexuaUy victimised themselves in chUdhood. It is perhaps appropriate to briefly outline the results o f those studies with more methodological problems first, to identify their short-comings, and then progress towards those with more robust designs and hence more meaningful

results.

3.2.2.1 Studies with methodological problems

Those studies fi*om which the fewest conclusions can be drawn were conducted with groups containing different types o f sex offenders (e.g. male incest, male chUd molesters, unspecified mixture o f ‘sex offenders’) and did not involve any comparison groups.

Studies such as these, conducted in the United States, reported proportions o f offenders abused in childhood ranging in males from 8% (Adler & Schütz, 1995) to 75% (Romano & De Luca, 1997), and in females from 38.5% (Allen & Lee, 1992) to 100% (Hunter et al, 1993).

Research conducted in the UK has reported abused proportions consistent with these figures. Browne, Foreman and Middleton (1998) studied a sample o f 96 male child sex offenders who were attending a community based Sex Offender Treatment Unit. They reported that 43% o f the sample had either been sexually or physically abused as a child, although the sexually abused proportion on its own was not stated. Waterhouse, Dobash and Camie (1994) gathered data on 501 cases o f child sexual abuse, which represented all such cases held at the start o f the study by a range o f agencies in Scotland. The agencies included social work departments, prisons, police services and hospitals. From files held by these agencies, it was possible to establish the childhood sexual abuse history o f 209 o f the perpetrators in these cases. It was found that 17% had e?q)erienced sexual abuse as children, either on its own (12%) or in coiyunction with physical abuse (5%). However the authors rightly advise caution when interpreting these results as data were available for so few (42%) o f the original total sample.

Finally, in an interview study o f 91 convicted child sex offenders (Elliott, Browne & Kilcoyne, 1995), 68% o f the particÿants stated that they had been sexually abused as children, although this included non-contact abuse. Contact sexual abuse was reported by 59% o f the sample.

Child sex offenders therefore appear to represent a group with, on the whole, high proportions o f childhood sexual victimisation. However, without any comparison groups, the strength o f any association between offence status and prior victimisation cannot be gauged.

There are a number o f studies that did report both the proportions o f sex offenders who were victims of abuse and comparison proportions for other groups (e.g. non-sex offenders or non offenders). Four out o f the six studies that compared the proportions o f adult male child molesters with those of non-sex offenders found that rates o f childhood abuse were significantly higher for the sex offenders than for the comparison groups (see Table 3.1). Similarly, two out of three studies A^tich compared the proportions o f adolescent sex offenders with adolescent non-sex offenders found a significant difference between them (see Table 3.2). These studies therefore provide reasonable support for an association between victimisation and subsequent perpetration.

The use o f at least one comparison group in these studies makes it possible to assess the meaning o f the quoted proportions, and to evaluate the strength o f the association between sexual victimisation in childhood and subsequent perpetration. Although many studies reported a significance value for the difference in proportions between the groups, very few calculated the strength o f the association with an appropriate statistic (e.g. odds ratio).

In addition to the problems highlighted earlier, there are three further methodological weaknesses in the research described above. First, all o f these studies involved the retrospective self-report o f subjects’ sexual victimisation and it was not clear whether the authors had established that the victimisation experience always preceded the onset o f their perpetrating behaviour. Second, very few o f the studies made a serious attempt to

Table 3.1 Self-reported sexual victimisation in childhood among adult male sex offenders and non-sex offending groups

Authors Proportion of Perpetrator sample(s) abused Proportion of Comparison group(s) abused Reported signifîcance Craissati & McClurg (1996)

Child molesters [n=80] 51% Violent offenders [n=20] 15%

Property offenders [n=20] 5%

p<.001

Dhawan & Marshall (1996)

Child molesters [n=i6] 50% Non offenders [n=20] 20% p<.05

Haywood et al. (1996) Child molesters: Clerics [n=24] 21% Non-clerics [n=45] 49% Non offenders: Clerics [n=4s] 4% Non-clerics [n=40] 15% OR = 6.05 (CI=1.08-33.96) OR = 5.42 (01=1.90-15.43)

Lang & Langevin (1991)

Heterosexual paedophiles [n=66] 45% Homosexual paedophiles [irf9] 55% Incest offenders [n=36] 50%

Non offenders (volunteers)

[o=50] 0%

p<.0001

Marshall & Mazzucco (1995)

Child molesters [n=24] 41.7% Non sex offenders [n=23] 8.7% p<.05

Table 3.2 Self-reported sexual victimisation in childhood among adolescent male sex offenders and non-sex offending groups

Authors Proportion of Perpetrator sample(s) abused Proportion of Comparison group(s) abused Reported significance of difference

Awad & Saunders (1991)

Child molesters [n=45]: 21% Sexual assaulters [n=49]: 4%

Delinquents [n=24] 0% p<.001

Ford & Linney (1995)

Child molesters [n=2i]: 52.2%

Rapists [n=i4]: 17.4%

Violent offenders [n=26] 17.4% Status offenders [n=2i] 13.0%

p<.01

Benoit & Kennedy (1992)

Child molesters of girls [n=^5]: 16% Child mois, of mainly boys [n=25]: 36%

Non-aggressive and Aggressive offenders [n=50]: 8%

ns p>.01

rule out other variables that might account for the development o f sexual abuse perpetration. A number matched the groups by the more basic fectors such as sample gender, age, or even socioeconomic status, but few measured other maltreatment experiences that were concurrent with the sexual victimisation (e.g. physical abuse, neglect), which might play a greater role in the subsequent development o f sexually abusive behaviour. Many o f those studies that did measure these Actors, and found that the groups significantly differed with respect to some o f them, did not subsequently control for their effects when assessing the significance o f the association between sexual victimisation and perpetration (Craissati & McClurg, 1996; Dhawan & Marshall, 1996; Ford & Linney, 1995; Lang & Langevin, 1991). It is therefore possible that in these studies, the relationship found between victimisation and perpetration was spurious.

Two studies did involve the measurement o f such additional variables. Awad and Saunders (1991) compared the experience o f physical abuse, social isolation and the anti­ social behaviour o f groups o f child molesters (n=45), sexual assaulters (n=49) and juvenile delinquents (n=24), whilst Marshall and Mazzucco (1995) compared child molesters (n=24) and non perpetrators (n=23) for their experiences o f similar maltreatment variables. Neither study established significant differences between the groups on these variables. Given the relative methodological sophistication o f these studies, more weight can be placed on their findings than on other studies.

A third methodological problem besets all o f the above studies and that is the nature o f the populations from which the groups were drawn. There is a practical difficulty in identifying a large enough group o f child molesters or other sex offenders to allow sufficient power for any significance calculations to be made. As a result, researchers tend to employ samples from clinics, secure units or prisons where there are previously identified groups o f such individuals. It is questionable, however, that these groups are representative o f the general population o f child molesters or other sex offenders who have never been convicted or even arrested for this behaviour.

To avoid this problem, the following group o f studies were conducted, from which more valid conclusions about the general population o f child molesters can be drawn.

3.2,2.2 Studies employing community samples

A further group o f studies have involved samples drawn from the community. Since the base rate o f sexual perpetrators is relatively low in the general population, this requires large numbers o f subjects to be screened to identify a small number o f such individuals. However the benefit is that the resulting sanq)le is, by definition, representative o f the general population o f sex offenders. The findings are therefore more widely applicable.

There have been eight studies involving community samples, which have examined the relationship between sexual victimisation and perpetration. However, not all o f these drew their samples from the same population, nor investigated exactly the same question. For example with regard to the samples, some studies questioned only college students (e.g. Fischer, 1992) whilst others used samples from large longitudinal cohorts (e.g. Borowsky, Hogan & Ireland, 1997). With regard to the research questions, some examined the relationship between childhood abuse and adult rape o f females (Koss & Dinero, 1989) whilst others took sexual molestation o f children as the outcome variable and looked at its relationship to prior victimisation (Bagley, Wood & Young, 1994).

One study that addressed this latter issue involved dividing a group o f 582 adolescent males into sexual perpetrators and non perpetrators and then establishing the sexual victimisation rates in each group (Fromuth, Burkhart & Webb Jones, 1991). Perpetration was defined as either contact or non contact sexual abuse o f a child whilst the definition o f victimisation was that employed by Finkelhor (1979). This requires that the perpetrator be over 16 years o f age. When such a definition was used, no difference was found in the victimisation rates o f the two groups suggesting no relationship between victimisation and perpetration However, it was argued that this definition was over restrictive, given that there may have been perpetrators who, whilst still under 16 years, sexually abused subjects who were at least 4 or 5 years younger than the perpetrators. Thus there may

Three points should be emphasised in relation to these findings, however. First, ‘sexual interest or activity’ does not equate to ‘sexual activity’. Le. there is a substantial difference between expressing a sexual interest in children and actually perpetrating sexual abuse on them. Factors that predict the former may not predict the latter. Second, the regression resulted in an association being found between the duration o f the abuse and the outcome, explicitly not the severity o f the abuse and the outcome. This relationship was found to he non-significant (p>.05). Third, the amount o f variance accounted for by the experience o f childhood sexual victimisation is very small This begs a question about what other factors may be involved in the development o f this behaviour.

Briere and Runtz (1989) also employed an outcome that involved an expression o f sexual interest in children, rather than a direct assessment o f perpetrating behaviour. Male subjects (n = 193) were asked to rate the likelihood o f them having sex with a child if they could be sure they would never be found out or punished. Their ratings were made on a five point Likert scale (1 = very likely, 5 = not likely), but these scores were recoded into a dichotomous classification. Those who rated themselves between levels 1 and 4 were reclassified as having a sexual interest in children, whilst only those who gave themselves a 5 rating were thought to have no interest in children. This appears to be over inclusive. The definition used for prior victimisation also gives cause for concern, being based on having ‘bad sex experiences’ when young. This could relate to sex with peers as well as with sexual perpetrators and therefore appears too broad a definition to allow meaningful conclusions to be drawn fi*om this study. Bearing these concerns in mind, Briere and Runtz did find that those with negative early sexual experiences rated themselves as more likely to have sex with children if they were never found out (p =

.011).

The five remaining community studies focused either on perpetrators against adult victims (Koss & Dinero, 1989) or against a mixture o f adult and child victims, i.e. no victim age was specified (e.g. Stevenson & Gajarsky, 1991). All except one (Fischer,

1992) found a statistically significant association between their measures o f sexual victimisation and perpetration. The study for which the relationship was not significant involved a sample o f 796 male and female college students. Many o f the other studies have reported proportions separately for males and females and have found the association to be stronger for males than for females. One possibility, therefore, for the lack o f a significant relationship in the Fischer study is that the presence o f females in the sample might have reduced the strength o f the overall association to below the level o f statistical significance.

A final community study, worthy o f more detailed description, involved the analysis o f data relating to several variables in addition to subjects’ sexual abuse histories and perpetrating behaviour (Borowsky, Hogan & Ireland, 1997). The data were taken firom the Minnesota Student Survey, a self-report survey for 71 594 high school pupils (9**^ and 12*** grade) concerning their experience o f various risk and protective fectors for sexually abusive behaviour. If the additional variables, including physical abuse, witnessing abuse and discontinuity o f care, were found to covaiy with sexual victimisation, they would represent possible alternative e?q)lanations for the apparent association between victimisation and perpetration. However, when the effects o f these variables were controlled in a logistic regression, the relationship between sexual victimisation and perpetrating behaviour was still statistical^ significant. This was the case for both male and female subjects and whether the subjects were abused ly a femily member or by non­ family, although the association was marginally stronger for males and for subjects abused by family (see Table 3.3).

Table 3 3 : Association between sexual victimisation and sexual perpetration (Borowsky et a l, 1997)

Male subjects

(Odds ratios and 95% confidence intervals)

Female subjects

(Odds ratios and 95% confidence intervals)

Intrafamilial sexual abuse 2.71, 1 .9 5 -3 .7 8 1.53, 1 .1 1 -2 .1 0

Extrafamilial sexual abuse 2.36, 1 .8 6 -3 .0 2 1.51, 1 .1 6 -1 .9 7

This last study provides perhaps the strongest evidence o f all those described so far in this section for the association between sexual victimisation and perpetration. However it should be stated that the definition used for sexual perpetration in this study does not distinguish between the sexual abuse o f adults and children. It also includes cases of verbal coercion rather than just physical coercion. This results in a heterogeneous group o f sex offenders making it difficult to draw clear conclusions fi*om the study.

It remains the case that all o f the studies reviewed so far employed a retrospective design and, as explained in the introduction to this section, this further limits the interpretations that can be made fi-om the data. To briefly reiterate these problems, they are first that whilst it is crucial that the risk factor preceded the outcome, there is no way o f reliably