Summary of findings

We found a strong association of psychosis with childhood sexual abuse, particularly when it involved sexual intercourse. This was maintained after adjustment for a range of sociodemographic variables. The association was not mediated by heavy cannabis use or by revictimisation experiences, although there did seem to be partial mediation by affect. Revictimisation had relatively little impact on the already strong association of childhood sexual intercourse with psychosis, but it magnified that of contact sexual abuse. In this sample the link between sexual abuse and psychosis was stronger in women.

Methodological limitations

The use of a random sample of the population removes nosocomial bias, but differential participation rates may distort the prevalence of psychosis and of sexual abuse, and the relationship between them. The most likely effect would be to reduce the prevalence of both elements, but it is not clear what effect this would have on their interrelationship, except in reducing statistical power. At 57%, the response rate in APMS 2007 was less than in earlier surveys in the National Survey programme. ^{Reference Jenkins, Meltzer, Bebbington, Brugha, Farrell and McManus17} We therefore conducted a sensitivity analysis to see if this level of refusal might affect the prevalence of sexual abuse. We dichotomised the sample according to the response rates seen in individual regions. We then used this new locational variable to compare the rates of endorsement of the computer-assisted personal interviewing sexual abuse question. There was no significant association between location and prevalence. Nor was this the result of a lack of statistical power: the prevalence of abuse was very similar in the lower and higher responding areas (5.5% and 4.9% respectively, P = 0.283).

Just over half of those with psychosis had been diagnosed under the gold standard conditions of SCAN, whereas the rest were diagnosed by a score of over two on our screening procedures. Using the screening results in this way would have identified 19 of the 23 individuals identified by SCAN in any case. Thus the two methods produced closely overlapping outcomes, which we feel justifies our use of the category of probable psychosis in the current analyses.

For various reasons, accounts of sexual abuse may not be wholly accurate, although it is difficult to say how inaccurate. Such enquiry is particularly sensitive, although not everyone is equally subject to embarrassment or discomfiture. Sensitivity is likely to vary with time, and possibly with age. Some of the more minor forms of abuse might be forgotten, discounted or repressed with increasing age and changing perspective. Our category of uncomfortable sexual talk might be particularly subject to such distortion. Moreover, some specific forms of abuse would not have been identified by our questions, for instance intrusive exposure to pornography.

In contrast, non-consensual sexual intercourse is clearly abuse. It is thus more likely to be underreported than forgotten, and its acknowledgement will depend to an extent on the method of enquiry. The 2007 APMS involved strenuous efforts to maintain data quality, including stressing confidentiality and interviewing participants alone where feasible. In addition, there are particular advantages to computer-assisted self-completion interview, which generally elicits franker responses than face-to-face questioning. ^{Reference Tourangeau, Rips and Rasinski27} Thus, getting people to complete the questionnaire themselves on a laptop computer and making them aware that the interviewer would have no access to the answer was intended to encourage frankness. Even so, the way the questions were framed (i.e. in terms of consent) might lead to underestimation of abuse. Abused people might think they had in fact consented in some way, particularly if they had been groomed, or thought themselves to blame for their predicament.

Although the information about abuse and disorder was obtained cross-sectionally, at a single point in time, in the overwhelming majority of cases childhood sexual abuse ostensibly pre-dates what are, after all, current disorders. A causal inference is consequently easier to defend for childhood sexual abuse than for adult sexual abuse. It is, however, still subject to the caveat of systematic distortion of reportage, in whatever direction, by people with mental disorders. Counter to this, empirical research has generally found them to be reliable informants. Fergusson et al ^{Reference Fergusson, Horwood and Woodward28} assessed the stability of reports of childhood sexual abuse over a 3-year gap. They concluded that people who had not been abused did not falsely report otherwise. However, positive reports were unstable; false negatives may reach 50%. Nevertheless, this did not materially affect estimates of the relative risk of associated psychiatric disorders. Set against this, there have been specific concerns about the reliability of reports of abuse in people affected by schizophrenia. However, Goodman et al ^{Reference Goodman, Thompson, Weinfurt, Corl, Acker and Mueser29} showed that their accounts were consistent over time, and concluded that the information obtained is sufficiently reliable to allow research in this area. Similar results have been reported by Fisher and colleagues. ^{Reference Fisher, Craig, Fearon, Morgan, Dazzan and Lappin30} Interestingly, they found that in 98% of individuals, the abuse preceded the psychosis.

Finally, confounding is a possibility, both for the basic analyses and for those involving mediation and moderation. We adjusted for sociodemographic variables, but these largely related to current, or a least adult, status. Thus educational level, income, and current social class relate to a date later than that of childhood sexual abuse, and would only have the power to confound if they served as proxies for lost opportunities in childhood. The impact of sexual abuse is likely to be greater than that of unspecified deprivation or poor parenting. However, although sexual abuse is likely to be strongly related to poor parenting, the reverse may not be true, so poor upbringing experiences may have separate effects. Upbringing arrangements provided the only proxy for poor parenting available to us in this study. However, there may of course be positive as well as negative effects of parental separation. Thus it was notable that not being brought up by both biological parents until 16 was no longer associated with psychosis when it was analysed together with abuse.

Sexual abuse and psychosis

The associations between reported childhood sexual abuse and probable psychosis were strong. In particular, the odds ratio linking psychosis with non-consensual sexual intercourse was over 10, with a PAF of 14%. It must be noted that the PAF is a statistical measure subject to the same reservations about causality as measures of association. Moreover, even with a large population sample, the confidence limits for the odds ratios are inevitably quite wide. Nevertheless, the values are at least suggestive of a major contribution of childhood sexual abuse to psychotic disorders.

Our findings were strongly moderated by gender, such that the link between sexual abuse and psychosis was far stronger in females. This is consistent with evidence from Myin-Germeys & Krabbendam ^{Reference Myin-Germeys and Krabbendam31} that psychosis in females is a more socially reactive condition than in males. However, we must add a caveat. The distribution of psychosis by gender was different in the 2000 British Psychiatric Morbidity Survey, being identified in 30 males and 30 females. ^{Reference Singleton, Bumpstead, O'Brien, Lee and Meltzer32} The relatively few cases of psychosis in males in the current study may have distorted our findings. Although in the 2000 survey information on sexual abuse was obtained in a different manner, with less precise dating, ^{Reference Bebbington, Bhugra, Brugha, Singleton, Farrell and Jenkins8} we were able to use it in an approximately equivalent analysis: this resulted in a non-significant abuse–gender interaction term, which did not replace the direct link between abuse and psychosis. Thus we must be cautious in placing weight on evidence of moderation in the 2007 survey.

Our results do support an emerging consensus linking childhood trauma with an increased risk of psychotic disorder or symptoms. This now comprises studies of increasing methodological sophistication, including some prospective studies. ^{Reference Bebbington, Bhugra, Brugha, Singleton, Farrell and Jenkins8,Reference Read, van Os, Morrison and Ross13,Reference Whitfield, Dube, Felitti and Anda33–Reference Shevlin, Dorahy and Adamson47} Our finding that most of the risk is conferred by the most severe form of childhood sexual abuse (i.e. non-consensual sexual intercourse) is novel: less severe abuse, such as touching and inappropriate talk, was not on its own associated with psychosis, although it most certainly is with other disorders. ^{Reference Jonas, Bebbington, McManus, Meltzer, Jenkins and Kuipers11} However, there are a number of ways of quantifying severity that were not available to us such as the frequency of abuse and abuse by multiple perpetrators. Other studies of psychosis have reported more in the way of a dose–response relationship, variously measured. ^{Reference Scott, Chant, Andrews, Martin and McGrath37,Reference Shevlin, Dorahy and Adamson38}

Mediation of the abuse–psychosis relationship

Sexual abuse in childhood is almost always an earlier event than the development of psychosis (the latter rarely emerges before 16, the cut-off age used here to denote childhood sexual abuse). Any causal link between the two must therefore involve mediation, often operating over a considerable interval. From a theoretical perspective, it is relatively easy to conceive of experiential variables such as childhood sexual abuse leading directly to mental representations and dispositions that set a course for the subsequent development even of a complex mental disorder such as psychosis.

The design of the current study limits both our choice of possible mediators, and the weight we can place on our analyses. We were able to examine revictimisation, heavy stimulant drug use, anxiety and depression.

Mediation by affect

Our analyses are in line with mediation effects for the affective consequences of childhood sexual abuse. The relationship between childhood sexual abuse and probable psychosis was reduced by adjustment for affect, albeit remaining significant, except when depression was controlled in relation to contact abuse. Whereas depression and anxiety showed roughly equivalent effects, when they were entered into the analysis together, the effect of anxiety became non-significant, suggesting that depression had the greater relevance. Adjustment for potential sociodemographic confounders had no effect on the results. There is an assumption built into the use of current affective state (our measures were related to the week preceding interview), which is that the state measures can be used as an adequate indicator of a propensity to dysphoria. It is only the latter that could stand as a mediator. Factor analyses have suggested that abuse is associated with anxiety, and that anxiety is in turn associated with more severe symptoms, including the development and persistence of positive symptoms of psychosis. ^{Reference Lysaker, Davis, Gatton and Herman48–Reference Garety, Bebbington, Fowler, Freeman and Kuipers50} Such pathways are amenable to empirical testing, preferably by longitudinal studies, and to psychological intervention.

Revictimisation and psychosis

Somewhat surprisingly, for revictimisation, only the broader category represented by contact abuse after 16 met criteria for being a potential mediator. Non-consensual sexual intercourse after the age of 16 did not do so, as it was unrelated to psychosis. This discrepancy invites caution, as contact not involving sexual intercourse may be more subject to distortion of recall by psychiatric state. This result is in contrast with the findings of Read et al. ^{Reference Read, Agar, Argyle and Aderhold51}

Although revictimisation (however defined) did not meet criteria for mediation, the association between childhood sexual abuse and probable psychosis seemed to be augmented by revictimisation of either sort. Note that our definition of revictimisation was based only on the repetition of childhood abuse in adulthood. Thus it could not identify multiple abuse restricted either to childhood or to adulthood, and would therefore tend to underestimate the frequency and impact of multiple abuse over the life course.

The existing literature provides context for these findings: childhood sexual abuse is strongly associated with revictimisation, ^{Reference Classen, Palesh and Aggarwal52} people who are abused as adults have higher rates of mental illness, especially schizophrenia, and psychiatric patients suffer significantly higher levels of adult abuse. ^{Reference Cloitre, Rosenberg, Follette and Ruzek53,Reference Goodman, Salyers, Mueser, Rosenberg, Swartz and Essock54} The relationship between sexual abuse and psychosis thus appears to be associated alike with the severity and the repetition of abuse. However, revictimisation may merely be a marker for severity of abuse. It is also possible that this apparent relationship is the result of confounding by abuse that is secondary to adult mental illness.

Heavy cannabis use

In this data-set, there appeared to be no links between heavy use of cannabis and either childhood sexual abuse or psychosis. The lack of association with psychosis is surprising in view of the wide interest in this link in the clinical and scientific community and the findings of other researchers. ^{Reference Moore, Zammit, Lingford-Hughes, Barnes, Jones and Burke21,Reference Harley, Kelleher, Clarke, Lynch, Arseneault and Connor55} It has been argued that adolescence may be a critical period, but we had no way of identifying people who were using cannabis heavily in adolescence. Some authors have, however, recently suggested that the link may not be so important at the population level. ^{Reference Hickman, Vickerman, Macleod, Lewis, Zammit and Kirkbride56} Although there may be issues of reportage in our data-set, they would seem unlikely to explain our very clear findings, particularly as there is little stigma attached to cannabis use in the general population of the UK.

The pathways to psychosis

Although we found evidence that anxiety and depression may mediate the psychosis–abuse relationship, many other candidates have been proposed. Our results certainly leave room for these, and the utility of complex models in driving research is thus maintained. ^{Reference Garety, Freeman, Jolley, Dunn, Bebbington and Fowler49,Reference Garety, Bebbington, Fowler, Freeman and Kuipers50,Reference Garety, Kuipers, Fowler, Freeman and Bebbington57} Likely candidates are mentally intrusive reminders of the abusive experience; the development of unhelpful psychological processes involving attitudes and beliefs, such as mistrust of others; styles of coping that may impair the processing of the original abuse; and enhanced propensities towards mood dysregulation in the face of subsequent experience. Severe trauma may also persistently modify the physiological stress response in deleterious ways. ^{Reference Read, van Os, Morrison and Ross13,Reference Heim, Newport, Miller and Nemeroff58} One putative pathway is that childhood sexual abuse sets up fundamental but dysfunctional schemas about oneself and the world – that the world is a dangerous place, that one is blameworthy or has no one to help. Childhood sexual abuse is often reported by victims as being accompanied by requirements for secrecy, and threats if the secret is broken. Thus no alternative views or explanations can be sought to refute such schemas. Childhood sexual abuse does seem to have disastrous effects on self-esteem and psychological well-being, ^{Reference Kamsner and McCabe59–Reference Murthi and Espelage61} and results in self-blaming attributions. ^{Reference Mannarino and Cohen62} It is also linked to paranoia and suspiciousness in non-clinical samples. ^{Reference Steel, Marzillier, Fearon and Ruddle63}

Such cognitive and affective attributes are also characteristics of psychosis, ^{Reference Fowler, Freeman, Smith, Kuipers, Bebbington and Bashforth64} are associated with the development of ‘at risk’ mental states, ^{Reference Birchwood65} and maintain positive symptoms in those who already have them. ^{Reference Garety, Bebbington, Fowler, Freeman and Kuipers50,Reference Garety, Kuipers, Fowler, Freeman and Bebbington57,Reference Kuipers, Garety, Fowler, Freeman, Dunn and Bebbington66–Reference Smith, Fowler, Freeman, Bebbington, Bashforth and Garety68} It seems likely that the pre-setting of emotional dysfunction and negative schemas provides an easily triggered automatic negative cognitive pathway. Along this pathway, further life events and stresses will lead to unusual experiences and emotional problems, which can be appraised as external and then understood as symptoms of psychosis. ^{Reference Garety, Kuipers, Fowler, Freeman and Bebbington57} Likewise avoidant coping is prominent both in survivors of sexual abuse and people with psychosis, and is therefore a candidate for the mediation process. ^{Reference O'Leary69,Reference Cooke, Peters, Fannon, Anilkumar, Aasen and Kuipers70} It appears to prevent the resolution of dysfunctional cognitions. Early sexual abuse may block effective social engagement, and lead to an isolation that may itself favour the development of psychotic symptoms. ^{Reference White, Bebbington, Pearson, Johnson and Ellis71} Thus the mediation of the link between childhood sexual abuse and psychosis is likely to be multifarious and complex. Whereas our demonstration of a mediating role for affect must be treated with reservation, it is consistent with a number of other studies.

Implications for intervention

Our findings have important implications for social and health policy. People who have experienced sexual abuse are often identified by Social Services and through the criminal justice system. There is also increasing awareness in schools and in primary care. There are thus opportunities for targeted primary and secondary prevention through dealing with the psychological consequences of abuse before psychiatric disorders emerge.

The damage brought about by an experience of sexual abuse will often be hidden by abused persons: although they will usually reveal it to clinicians, it is likely to require questioning that is both direct and sensitive. Such enquiry is an important component of psychiatric treatment and management, ^{Reference Holmes, Arntz and Smucker72} particularly as there is now an argument for introducing specific techniques such as imagery re-scripting ^{Reference Read, Hammersley and Rudegeair73,Reference Linden and Zehner74} into the cognitive–behavioural treatment of psychosis.