Schizophrenia is characterised by a breakdown of thought processes and impairment of emotions. It most commonly manifests itself through positive symptoms (auditory hallucinations, paranoid or bizarre delusions) disorganisation (disorganised speech and thinking) and negative symptoms (flat mood and emotion, poverty of speech, inability to experience pleasure, and lack of motivation). It is accompanied by significant social or occupational dysfunction. The onset of symptoms typically occurs in young adulthood, with a worldwide lifetime prevalence of about 0.3–0.7%. Diagnosis is based on observed behavior and the patient's reported experiences.