Cannon M. Prevalence of psychotic symptoms in childhood and adolescence: a systematic review and meta-analysis of population-based studies. Psychological Medicine. 2012; 9:1-7. AuthorsIan Kelleher, Dearbhla Connor, Mary C. Clarke, Nina Devlin, Michelle Harley, and Mary Cannon This article is available at e-publications@RCSI: http://epubs.rcsi.ie/psychart/1 -Use LicenceAttribution-Non-Commercial-ShareAlike 1.0 You are free:• to copy, distribute, display, and perform the work.• to make derivative works. Under the following conditions:• Attribution -You must give the original author credit.• Non-Commercial -You may not use this work for commercial purposes.• Share Alike -If you alter, transform, or build upon this work, you may distribute the resulting work only under a licence identical to this one.

Hallucinations and delusions, the classic symptoms of psychosis, have recently been documented to occur at a much higher prevalence in the general population than clinically diagnosed psychotic disorder.1 A meta-analysis of prevalence studies of psychotic symptoms in young people demonstrated a median prevalence of 17% in children aged 9-12 years and 7.5% in adolescents aged 13-18 years.2 As the term suggests, psychotic symptoms have typically been considered to relate to psychotic disorder. Indeed, research has shown that members of the general population who report psychotic symptoms share a wide range of risk factors with people with schizophrenia (see Kelleher & Cannon for review), [3][4][5][6][7][8][9] and young people who report psychotic symptoms have been found to be at increased risk of psychotic disorder in adulthood.10,11 Individuals who report psychotic symptoms are also more likely to report non-psychotic psychopathological symptoms, especially symptoms of depression; [12][13][14][15][16] Yung et al, for example, reported that individuals who had a diagnosed depressive disorder endorsed an increased number of psychotic symptoms on the Community Assessment of Psychic Experiences questionnaire compared with controls.17 Bartels-Velthuis et al found that young adolescents who disclosed psychotic symptoms were approximately 3-5 times more likely to score in the clinical psychopathology range on the parent-completed Child Behavior Checklist. Community-based studies to date, however, have relied mainly upon questionnaires to assess psychotic symptoms and have involved limited data on non-psychotic psychopathology. In addition, although research suggests that psychotic symptoms are more common in younger than in older children, 2 there is a lack of information on whether there are differences in the clinical significance of psychotic symptoms across different stages of adolescence. In an attempt to improve our understanding of the clinical significance of psychotic symptoms in the general population we examined data from four population studies, comprising two large population surveys and two in-depth clinical interview studies of psychotic symptoms. The aims of this work were to investigate whether psychotic symptoms predicted nonpsychotic clinical diagnoses, and if so, which disorders; to investigate whether psychotic symptoms predicted more clinically severe disorder in terms of comorbid psychopathology (i.e. having more than one diagnosis); and to investigate whether the significance of psychotic symptoms varied as a function of age. MethodSurvey studies Background Epidemiological research has shown that hallucinations and delusions, the classic symptoms of psychosis, are far more prevalent in the population than actual psychotic disorder. These symptoms are especially prevalent in childhood and adolescence. Longitudinal research has demonstrated that psychotic symptoms in adolescence increase the risk of psychotic disorder in adulthood. There has been a lack of research, however, on the immediate clini...

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Recent research shows that psychotic symptoms, or psychotic-like experiences (PLEs), are reported not only by psychosis patients but also by healthy members of the general population. Healthy individuals who report these symptoms are considered to represent a non-clinical psychosis phenotype, and have been demonstrated to be at increased risk of schizophrenia-spectrum disorder. Converging research now shows that this non-clinical psychosis phenotype is familial, heritable and covaries with familial schizophrenia-spectrum disorder. A review of the research also shows that the non-clinical phenotype is associated extensively with schizophrenia-related risk factors, including social, environmental, substance use, obstetric, developmental, anatomical, motor, cognitive, linguistic, intellectual and psychopathological risk factors. The criterion and construct validity of the non-clinical psychosis phenotype with schizophrenia demonstrates that it is a valid population in which to study the aetiology of psychosis. Furthermore, it suggests shared genetic variation between the clinical and non-clinical phenotypes. Much remains to be learned about psychosis by broadening the scope of research to include the non-clinical psychosis phenotype.

Individuals who report psychotic-like experiences are at increased risk of future clinical psychotic disorder. They constitute a unique "high-risk" group for studying the developmental trajectory to schizophrenia and related illnesses. Previous research has used screening instruments to identify this high-risk group, but the validity of these instruments has not yet been established. We administered a screening questionnaire with 7 items designed to assess psychotic-like experiences to 334 adolescents aged 11-13 years. Detailed clinical interviews were subsequently carried out with a sample of these adolescents. We calculated sensitivity and specificity and positive predictive value (PPV) and negative predictive value (NPV) for each screening question for the specific symptom it enquired about and also in relation to any psychotic-like experience. The predictive power varied substantially between items, with the question on auditory hallucinations ("Have you ever heard voices or sounds that no one else can hear?") providing the best predictive power. For interview-verified auditory hallucinations specifically, this question had a PPV of 71.4% and an NPV of 90.4%. When assessed for its predictive power for any psychotic-like experience (including, but not limited to, auditory hallucinations), it provided a PPV of 100% and an NPV of 88.4%. Two further questions-relating to visual hallucinations and paranoid thoughts-also demonstrated good predictive power for psychotic-like experiences. Our results suggest that it may be possible to screen the general adolescent population for psychotic-like experiences with a high degree of accuracy using a short self-report questionnaire.