Prospective investigations of the prodromal state of schizophrenia: review of studies.Objective: The paper presents a comprehensive overview of prospective studies monitoring or intervening in the pre-onset phase of first episode psychosis. Method: A systematic literature search was conducted and supplemented by a manual search. All relevant studies were ordered and intensively reviewed according to specified criteria. Methodological and conceptual issues are discussed. Results: Reports of 23 prospective studies were found, some describing subsamples of larger samples. Major methodological and conceptual divergences exist. Conclusion: Applied criteria detect individuals with a significantly increased risk of psychosis within the schizophrenia spectrum, but these criteria are only validated on clinical populations. The significance of differences in sample-characteristics is unclear. Most study samples are small. Results are preliminary and in need of further research before they constitute a realistic knowledge base. Methodological and conceptual issues should not be underestimated. Summations• Current research has defined new specific criteria for samples with increased risk of psychosis. The samples linked to these criteria are systematically reviewed. • Transition rates are difficult to compare because of different intake criteria and composition of sample-subgroups. • It is still uncertain whether treatment at this stage may prevent full-blown psychosis, but the persons are generally ill and in need of psychiatric/psychological help. • Conceptual issues arise from the use of the term ÔprodromalÕ. Considerations• Results of current studies are mainly preliminary and cannot yet provide general guidelines for clinical practice. • Samples are apt to be symptomatologically, phenomenologically and pathogenetically heterogeneous. • The concept of psychosis/schizophrenia is not clarified through the discussion of empirical results.• The studies are not reviewed for their statistical qualities.

The gender differences demonstrated in the study suggest gender specific treatment interventions in order to provide optimal treatment for both male and female patients.

The instruments detect individuals with an increased risk of psychosis in clinical populations, but predictive validity and measures of reliability is insufficiently evaluated. Studies including instruments from both traditions should be conducted, in order to obtain an empirical basis of hypothesized relations between instruments. Instruments elucidating phenomenological aspects of anomalies in self-experience may contribute with valuable data on the pre-onset phase of psychosis.