Self-reported psychotic experiences among the general Dutch population
Positive psychotic symptoms or experiences (i.e. hallucinations, delusions and disorganized speech) lie on a continuum that spans from normal to psychopathological experiences (Schultze-Lutter et al., 2022). The prevalence of psychotic experiences in the general population is estimated to be ~ 7% (Linscott & Van Os, 2013). Even though approximately 80 % of psychotic experiences are short-lived, 20% of the individuals that experience them proceed to develop persistent psychotic experiences and 7% develop a psychotic disorder (Van Os & Reininghaus, 2016). An international study of the prevalence of psychotic disorders established that approximately 11% of the general population in the Netherlands aged 18 to 95 years old had at least one psychotic experience during their lifetime and 3% during the past 12 months (McGrath et al., 2015). The data for this project was collected in 2002 and 2003 and psychotic experiences were measured with the Psychosis Module of the World Health Organization World Mental Health Composite International Diagnostic Interview (WHO WMH-CIDI) (McGrath et al., 2015). This module probes six types of psychotic experiences divided in hallucinations (auditory and visual), bizarre delusions (thought insertion/withdrawal and mind control/passivity) and paranoid delusions (ideas of reference and plot to harm/follow) (McGrath et al., 2015).
According to Van Os and Reininghaus (2016), psychotic experiences in the general population may indicate the behavioural manifestation of a distributed multifactorial risk for psychosis. The factors encompassed and shared by this “extended psychosis phenotype” are demographic, genetic, environmental and psychopathological ones (Van Os & Reininghaus, 2016). For example, associations have been found between psychotic experiences and younger age, female gender, being unmarried, being not employed, having a lower household income level and poorer quality of life (Linscott et al., 2013; McGrath et al., 2015; Wigman et al., 2017). Also associated with psychotic experiences are social withdrawal during childhood, traumatic life events, psychological abuse, psychiatric disorders such as mood and anxiety disorders, poor sleep quality, cannabis use, family history of mental illness and obstetric complications at birth (Bourgin et al., 2020; Cosgrave et al., 2021). Furthermore, culture can affect whether people report hallucinations, since culture can impact what is deemed, or not deemed, a hallucinatory experience (Laroi et al., 2014). Finally, a German study of psychotic-like experiences in the 20-60 year old general population found that women, compared to men, scored higher on psychotic like experiences, but lower on disorganized- and negative-like symptoms (i.e. symptoms that indicate loss of, or a decrease in, normal functions) (Unterrassner et al., 2017).
Within psychotic disorders, incidence rates differ between age groups and sex with rates peaking in men up until age 25 and declining sharply thereafter and a lower initial peak and more even distribution for women across the life course (Jongsma et al., 2018). A French study found that prevalence of psychotic disorders peaks between ages 35 and 49 in males, after which it decreases with age (Chan Chee et al., 2017). In females, prevalence is highest at age 50 and plateaus thereafter (Chan Chee et al., 2017). A systematic review showed that combined prevalence estimates of schizophrenia did not significantly differ between males and females (McGrath et al., 2008). Regarding psychotic experiences, a meta-analysis found no difference in prevalence rates between males and females, but did find that they are more common in younger people (Linscott et al., 2013).
Often, research on psychotic experiences in the general population is done without stratifying prevalence rates based on age or sex. If the age-sex distribution of psychotic experiences follows a similar pattern as in psychotic disorders, this could potentially strengthen the psychosis continuum theory. Furthermore, knowledge on which factors are associated with psychotic experiences could generate more phenomenological insight. To this end, a new study using Lifelines data will be conducted, in which the overall, and the age- and sex-specific prevalence rates of self-reported psychotic experiences among the general Dutch population will be researched, as well as their associated socio-demographic, behavioural, environmental, premorbid, family, diagnostic, health related, functioning and cognitive characteristics.