The current study set out to examine if cumulative traumas were associated with greater acknowledgment of psychosis symptoms in 2 nationally representative samples, one from the United States of America and the other from the United Kingdom. Results clearly demonstrate that multiple traumatic experiences were associated with an increased likelihood of psychosis. Although a single trauma type did not significantly increase the likelihood of psychosis, experiencing 2 or more types of trauma significantly increased the likelihood of psychosis, with dramatic increases associated with experiencing all trauma types. The findings pertinently demonstrate a dose-response relationship between trauma and psychosis in these nonclinical samples, with increases in psychosis likelihood associated with more trauma exposure. Prior work in representative general population samples had supported a link between multiple traumas and psychiatric illnesses, such as depression.5
The present results confirmed previous findings within the trauma and psychosis literature by using 2 large community samples and highlighted a dose-response effect with reference to trauma and the increased likelihood of psychosis. Of particular emphasis were interpersonal traumas, and interestingly, these general population samples indicate that more than 1 type of interpersonal trauma is required to increase the likelihood of reporting psychosis symptoms.
Although the dose-response association between the experience of traumas and psychosis was generally evident, the increase in the odds ratios was not entirely consistent for the BPMS. Specifically, the experience of 3 traumatic events resulted in a higher probability of psychosis than with 4 traumatic events. Yet, with this finding aside, the BPMS still showed a clear dose-response effect. Another interesting aspect of the results was that for both samples, the odds ratios associated with 5 traumas were very high relative to those for 4 traumas. For both the NCS and BPMS, the odds ratios associated with 5 traumas were similar or higher than the upper 95% confidence interval for 4 traumas. This suggests that although the relationships appear to be generally monotonic, they are not linear due to this large increase in effect size for 5 traumas.
The current study showed that for the NCS, the traumas most significantly associated to psychosis were molestation and physical abuse as a child. This is largely consistent with previous research in the area.32
Based on the BPMS, sexual abuse was the trauma with the strongest association with psychosis. Serious illness, injury or assault, and violence in the home were also statistically significant. Such associations have now been reported consistently using both clinical and nonclinical samples.18,19,33–35
The argument for a causal relationship has been further strengthened by the use of prospective studies10
or studies that do not rely on retrospective accounts of traumatic experiences.36
The current findings indicate the added risk of multiple traumas. A recent text provides a substantive review of the literature regarding the link between trauma and psychosis.37
The central challenge for future research is identifying and understanding the key mechanisms, which link increased trauma with psychosis symptoms. Cognitive models have identified the importance of misattributions, misinterpretations, and beliefs about psychosomatosensory experiences in the development and maintenance of psychosis symptoms, such as hallucinations and delusions.38–40
With a rediscovery of the effects of trauma on the body and on psychological as well as somatosensory systems, cumulative interpersonal traumas may heighten psychosomatosensory activation increasing the likelihood of etiologically significant misattributions, along with those that have a maintenance effect.41,42
Dissociation is another psychological variable proposed to link traumatic experience with especially positive psychotic symptoms.35,43–46
Hallucinations, for example, may be the consequence of a failure to integrate percepts with affective and cognitive representations of a traumatic event.47
More traumas would lead to more dissociation and therefore greater fragmentary representations of traumatic events, which may be experienced as hallucinations. These and other explanatory models require empirical assessment.
Alternatively, a Traumagenic Neurodevelopmental model8
has been proposed that suggests early traumatic life events can produce physiological changes that contribute to greater vulnerability to psychosis. In particular, this model proposes that stressful events produce activation of the hypothalamic-pituitary-adrenal (HPA) axis, which is associated with the release of glucocorticoids, which can subsequently impair the regulation of the HPA axis if exposure to traumatic experiences is prolonged. Such a process has also been implicated in the development of posttraumatic stress disorder48
(PTSD). This may account for the high rates of comorbid PTSD with psychosis,49,50
similarity of psychotic and PTSD symptoms51
and PTSD as a contributing factor in interactive models of psychosis.52,53
The limitations of using general population samples to infer potential relationships in clinical disorders, such as the psychoses, has been addressed elsewhere54
as has the type of methodology used here. Additionally, research has addressed the methodological issues associated with the reliability of retrospective self-report accounts of traumatic experiences and concluded that such reports are “surprisingly reliable.”9
(p334) Indeed, accurate histories have been reported by people with schizophrenia and other psychoses.8,55–58
An additional limitation of the present research is the possible underestimation of abuse. Previous research has shown that asking about “abuse” as opposed to asking specific questions regarding abuse can lead to lower rates of acknowledgement by around 50%.59
But a particular limitation of the current study, in light of the variables examined, is no specific age limit or age specificity for traumatic events. With no indication of trauma onset or the chronology of multiple traumas, no conclusions can be drawn on the developmental impact of trauma or at what point during development multiple traumas increase risk of psychosis symptom formation. In addition, the measure of cumulative traumatic experiences used in this study does not account for multiple same trauma experiences or individual differences in the severity of a particular trauma. The analysis also assumes that the effect of the different traumas is comparable.
The current study has demonstrated the relationship between multiple childhood and interpersonal trauma types and increased likelihood of experiencing psychosis symptoms in 2 large, representative, general population samples. As well as highlighting a dose-response relationship between trauma types and psychosis, these results further highlight the need for a thorough trauma assessment in individuals with psychotic illnesses. This increases the likelihood that, where appropriate, interventions can be psychologically formulated and driven. However, there remains a pressing need for a greater empirical understanding of the nature of, and difference between, psychosis associated with trauma and psychosis unassociated with trauma. Studies have tended to report trauma associated with a large number of psychotic individuals, but not all. Thus, there is no empirical foundation to suggest that trauma is an etiological risk factor for all psychoses. Consequently, different treatment strategies may be required for different psychotic presentations and etiological foundations. As this study alludes to, for some individuals, the impact of multiple childhood interpersonal traumas may be pertinent to both case formulation and treatment.