Young cases of schizophrenia identified in a national inpatient register--are the diagnoses valid?

Background: Psychiatric inpatient registers are often used in research in the Nordic countries. We aimed to investigate the validity of recorded diagnoses of schizophrenia in the Swedish National Inpatient Register, in cases of early age at onset. We also wanted to describe the accuracy of the diagnoses in cities/university clinics and country hospitals as well as in child and adolescent psychiatric clinics and clinics for adults.