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Background: Several psychological symptoms in adolescence associate with later development of psychosis. However, it is unclear which symptoms specifically predict psychotic disorders rather than psychiatric disorders in general. We conducted a prospective study comparing how specific adolescent psychotic-like symptoms, predicted psychotic and non-psychotic hospital-treated psychiatric disorders in the population-based Northern Finland Birth Cohort 1986 (NFBC1986). Methods: At age 15–16 years, 6632 members of the NFBC1986 completed the PROD-screen questionnaire. New hospital-treated mental disorders of the NFBC1986 participants were detected between age 17 and 30 years from the Finnish Care Register for Health Care. Multiple covariates were used in the analysis. Results: During the follow-up, 1.1% of the participants developed a psychotic and 3.2% a non-psychotic psychiatric disorder. Three symptoms were specifically associated with onset of psychosis compared to non-psychotic psychiatric disorders: ‘Difficulty in controlling one’s speech, behaviour or facial expression while communicating’ (adjusted OR 4.00; 95% CI 1.66–9.92), ‘Difficulties in understanding written text or heard speech’ (OR 2.25; 1.12–4.51), and ‘Difficulty or uncertainty in making contact with other people’ (OR 2.20; 1.03–4.67). Of these, the first one remained statistically significant after Bonferroni correction for multiple comparisons. Conclusions: To our knowledge, this is the first general-population-based prospective study exploring psychiatric symptoms predicting the onset of hospital-treated first-episode psychosis in comparison to non-psychotic disorders. We found three symptoms related with difficulties in social interaction which predicted onset of psychosis. This is a novel finding and should be replicated.

Objective: The aim of this study was to explore changes in the incidences of childhood and early adulthood hospital‐treated psychiatric disorders in five large Finnish birth cohorts of individuals born between 1966 and 1997. Methods: The five birth cohorts were as follows: Northern Finland Birth Cohort 1966 (NFBC 1966) and 1986 (NFBC 1986), 1987 Finnish Birth Cohort (FBC 1987) and 1997 (FBC 1997), and Finnish 1981 Birth Cohort Study (FBCS 1981). Incidences of hospital‐treated psychiatric disorders in each cohort were calculated separately for males (N = 71,209) and females (N = 65,190). Poisson regression was used to test difference in proportions of psychiatric disorders in wide range of diagnosis classes separately in childhood and adolescence, and early adulthood. Results: The total incidences of psychiatric disorders in childhood and adolescence among males has increased in the birth cohorts over decades (Incidence Rate Ratio, IRR = 1.04 (1.04–1.05); p < 0.001). Similar result was seen among females (IRR = 1.04 (1.03–1.04); p < 0.001). In early adulthood, there was significant increase among females (IRR = 1.04 (1.03–1.05);p < 0.001), but among males, the change was not significant (IRR = 0.99 (0.99–1.00), p = 0.051). Conclusions: The main finding was that the cumulative incidence of hospital‐treated psychiatric disorders increased over the decades in Finland. The increasing trend in hospital‐treated psychiatric disorders in early adulthood was detected in females but not in males. In the youngest cohorts, the cumulative incidence of hospital‐treated psychiatric disorders was at the same level in males and females, whereas in oldest cohort, males had higher incidence than females.