The current study found a high proportion of formally FP psychotic experiences in a large general population sample, comparing self-report with clinical interview. The present study also confirms earlier work11
that FP psychotic experiences have clinical and prognostic relevance. Compared with the control group, the FP group was more likely to have mood, anxiety, or substance use disorders, as well as higher levels of neuroticism. They also had higher rates of childhood trauma and peer victimization, were more likely to have experienced a negative life event in the past year, and to have ever used cannabis. They had worse physical and mental health, worse social functioning, and more symptomatic expression of depression and mania. Compared with those with confirmed psychotic experiences, however, associations with psychopathology, social functioning, environmental risk factors, and help seeking were generally weaker.
To the best of our knowledge, this is the first study to investigate the characteristics of individuals with FP psychotic experiences. It confirms the findings of earlier studies that self-report questionnaires for psychotic experiences yield high rates of formally FPs.9,10,31
The PPVs for hallucinations were higher than for delusions, which is also in line with previous research,10
possibly because questions about hallucinations may be less ambiguous than questions about delusions. Importantly, however, the current results also indicate that reporting a FP psychotic experience on a self-report measure may carry relevant risk-related psychometric information about an extended psychosis phenotype that is more likely to remain subclinical but may eventually also lead to need for care, as suggested by Bak and colleagues, who found that FP psychotic experiences predicted the subsequent development of psychotic disorder 3 years later.11
The reported effect sizes may therefore point to a continuum of behavioral expression of risk, as suggested by Poulton and colleagues.7
Indeed, probabilities of other psychopathology and environmental risk factors for psychotic disorder became successively higher with increasing certainty about the presence and nature of the reported experiences. The current study is an important addition to the NEMESIS-1 findings reported by Bak and colleagues as they found that FPs predicted future psychotic disorder but reported no additional characteristics of their FP group.
Compared with the FP group, the psychotic experiences of the TP group were more frequent and more recent. Furthermore, the TP group was about 4 times more likely to seek help for their psychotic experiences. This might represent the crucial difference between the FP and the TP group: the SRPEs were more likely to be confirmed by clinicians when they were more frequent and the individual had sought help for this experience. In a study by Brett and coworkers, evidence was found that underlying unhelpful metacognitive beliefs (that in turn were associated with anxiety and depression) were positively associated with help seeking for psychotic experiences32
. In line with these findings, the present study showed that the TP group, compared with the FP group, more often had anxiety and mood disorder diagnoses, which could account for the increased help-seeking behavior.
The results of this study should be interpreted in the context of its strengths and limitations. Strengths are the size and representativeness of the sample. The most important limitation is the lack of information on whether the FP group also has a higher risk of transition to psychotic disorder compared with the control group. This information should become available as part of the ongoing follow-up of the current sample. A further limitation is that the clinical interviews were only conducted in those individuals reporting a possible psychotic experience and that the interview only included questions about these experiences. The consequence of this choice was that there was only information on FP experiences, not false negatives. Therefore, it was not possible to investigate the sensitivity and specificity of the various psychotic experiences. Another limitation was the chosen method of reinterviews: because it was not feasible to visit the participants with SRPEs on a second occasion for the purpose of a clinical interview, it was chosen to conduct the reinterview over the telephone. It is possible that subtle nonverbal cues have been missed that would have been picked up in a face-to-face interview. However, this method was also used in NEMESIS-1 and findings from these telephone11
interviews reliably predicted future psychotic disorder 11, thus supporting its reliability.
In spite of these limitations, the present findings provide important clues about the characteristics of a subgroup of individuals presenting with experiences that may represent the mildest subthreshold expression of psychosis. Further study of this group may help to identify biological, psychological, and social processes underlying the first expression of psychotic symptoms, the persistence of these over time, and eventually, development of need for care.