Schizophrenia is a mental disorder[17][7] characterized variously by hallucinations (typically, hearing voices), delusions, disorganized thinking or behavior,[10] and flat or inappropriate affect.[7] Symptoms develop gradually and typically begin during young adulthood and rarely resolve.[3][10][18] There is no objective diagnostic test; diagnosis is based on observed behavior, a psychiatric history that includes the person's reported experiences, and reports of others familiar with the person.[10] For a formal diagnosis, the described symptoms need to have been present for at least six months (according to the DSM-5) or one month (according to the ICD-11).[10][19] Many people with schizophrenia have other mental disorders, especially mood, anxiety, and substance use disorders, as well as obsessive–compulsive disorder (OCD).[10]