Final answer:
A feature that would support the diagnosis of dysthymia in a 17-year-old with depressed mood, low self-esteem, and poor concentration is the duration of the symptoms.
Step-by-step explanation:
To support a diagnosis of dysthymia in a 17-year-old with depressed mood, low self-esteem, and poor concentration, a feature that would be important to consider is the duration of the symptoms. Dysthymia is a type of chronic depression that lasts for at least two years in adults, or one year in children and adolescents. Therefore, if the student has been experiencing these symptoms for an extended period of time, it would support the diagnosis of dysthymia.