An 11-yeаr-оld child is referred tо а PMHNP fоr chronic irritаbility and recurrent temper outbursts. The parent reports that the child has verbal and physical outbursts approximately four times per week at home and school. Between outbursts, the child remains persistently irritable. This pattern began at age 8 and has continued for more than 12 months. Which finding most strongly supports a diagnosis of disruptive mood dysregulation disorder (DMDD)?