Persons with bipolar disorder may receive different diagnoses depending on their symptoms and the severity of them. This has led some psychologists and psychiatrists to recommend that there is a spectrum of bipolar disorders with distinct but overlapping features. There is serious debate about the proper relationship between bipolar disorder and schizophrenia (first distinguished by Emil Kraepelin in the late 19th century), the related classification of schizoaffective disorder, and the relationship between bipolar disorder and major depressive disorder or unipolar disorder.