Psychotic-like experiences are more prevalent in the general population than clinical psychotic disorders, suggesting that these experiences may occur as part of a nonpathological phenotype, which lies on a continuum with psychotic disorder.1–3
A recent meta-analysis by van Os et al4
reported a median prevalence of about 5% for psychotic experiences in the general population. Data on adolescent populations indicate that rates of psychotic-like experiences may be even higher among this age group.1,5–8
Research on long-term outcomes suggests that individuals who report psychotic-like experiences are at significantly increased risk of clinical psychotic disorders.1,4,9
Among a New Zealand birth cohort, Poulton et al1
found that 11-year olds who reported psychotic symptoms were at a 5- to 16-fold specific increased risk of adult psychotic disorder. Welham et al10
have also documented that self-reported psychotic-like experiences (specifically, auditory hallucinations) at age 14 years are associated with increased risk for adulthood psychotic disorder, assessed aged 21 years. Hanssen et al9
found that, among a general population sample of 18- to 64-year olds, the 2-year transition rate to clinical psychotic disorder was more than 60 times higher for those who had previously reported psychotic-like experiences compared with those without incident psychotic experiences. Individuals who report psychotic-like experiences, then, represent a valuable population in studying the developmental trajectory to schizophrenia and related illnesses. This group can be conceptualized as representing a “pre-prodromal” population and provides a complementary approach to the ultra-high-risk prodromal strategy, which was pioneered in Melbourne, Australia, and has since been adopted in several centers worldwide.11–16
An accurate and rapid screening instrument for identifying this population would be valuable.
Many articles have reported on psychotic-like experiences as assessed by screening interviews or screening questionnaires.6,7,17–21
However, there have been mixed results from the 2 studies to date that have reported on the validity of these screening questions among adolescent populations. Laurens et al7
found only moderate agreement between their screener questionnaire and the results of a subsequent clinical interview in a random sample of their screened population. They reported kappa scores of between 0.16 and 0.65 for agreement between clinician and child on each of the screening questions, with most falling into either the “fair agreement” (0.21–0.40) or the “moderate agreement” range (0.41–0.60). Horwood et al21
also found that endorsement of their screener questions did not generally predict genuine psychotic symptoms when followed up by further probe questions.21
Positive predictive power for most questions was no more than 50%. One item, however, displayed some promise in terms of its positive predictive power; a screening question on “auditory hallucinations” attained a positive predictive value (PPV) of 70.6%, suggesting that such a question might be useful in identifying adolescents with psychotic-like experiences in the general population. However, due to the study design, they were not able to give any indication of the sensitivity of this question. Thus, the literature to date suggests a high rate of false positives when screening for psychotic experiences and gives no indication of the rate of false negatives. Further research is necessary to determine whether it is possible to sensitively and specifically screen for adolescents with psychotic-like experiences in the general population using self-report questionnaires.