The association between negative symptoms, psychotic experiences and later schizophrenia: A population-based longitudinal study

Background: Psychotic experiences are common in the general population, and predict later psychotic illness. Much less is known about negative symptoms in the general population. Method: This study utilized a sample of 4,914 Israel-born individuals aged 25-34 years who were screened for psychopathology in the 1980's. Though not designed to specifically assess negative symptoms, data were available on 9 self-report items representing avolition and social withdrawal, and on 5 interviewer-rated items assessing speech deficits, flat affect and poor hygiene. Psychotic experiences were assessed using the False Beliefs and Perceptions subscale of the Psychiatric Epidemiology Research Interview. Psychiatric hospitalization was ascertained 24 years later using a nation-wide psychiatric hospitalization registry. Results: After removing subjects with diagnosable psychotic disorders at baseline, 20.2%had at least one negative symptom. Negative symptoms were associated with increased risk of later schizophrenia only in the presence of strong (frequent) psychotic experiences (OR = 13.0, 9% CI: 2.1-79.4). Conclusions: Negative symptoms are common in the general population, though the majority of people with negative symptoms do not manifest a clinically diagnosed psychiatric disorder. Negative symptoms and psychotic experiences critically depend on each other's co-occurrence in increasing risk for later schizophrenia.