Epidemiological studies show that approximately 3.2% of children in the community have chronic problems with irritability and temper, the essential features of DMDD. These problems are probably more common among clinic-referred youths. Parents report that approximately 30% of children hospitalized for psychiatric problems meet diagnostic criteria for DMDD; 15% meet criteria based on the observations of hospital staff. Beginning in the 1990s, some clinicians began observing children with hyperactivity, irritability, and severe temper outbursts. These symptoms greatly interfered with their lives at home, school, and with friends. Because other diagnoses, like ADHD and ODD, did not capture the severity of children's irritability and anger, many of these children were diagnosed with bipolar disorder. Longitudinal studies showed that children with chronic irritability and temper outbursts often developed later problems with anxiety and depression, and rarely developed bipolar disorder in adolescence or adulthood. Consequently, the developers of DSM-5 created a new diagnostic label, DMDD, to describe children with persistent irritability and angry outbursts. In 2013, the American Psychiatric Association (APA) added DMDD to the DSM-5 and classified it as a depressive disorder.