Hallucinatory experiences and onset of psychotic disorder: evidence that the risk is mediated by delusion formation

Objective: To examine the hypothesis that the risk for onset of psychotic disorder in individuals with self-reported hallucinatory experiences (HE) would be higher in those who developed delusional ideation (DE) than in those who did not. Method: A population sample of 4673 individuals were interviewed with the Composite International Diagnostic Interview at baseline and 1 and 3 years later. At year 3, clinical re-interview took place to identify onset of psychotic disorder. Results: Given the presence of HEs at baseline, the increase in risk of having the psychosis outcome at year 3 was much higher in those with DE at year 1 than in those without DE (risk difference between individuals with and without DE: 18.72%, 95% CI: 2.22-35.23, chi(2) = 4.94, df = 1, P = 0.026). Conclusion: The results are in line with current psychological theories stating that clinical outcome of psychosis-like experiences is related to the development of secondary beliefs and appraisals.