170 Depressive Disorders
way”), they may not be reported unless the indi vidual is directly prom pted. During the 2-year
period (1 year for children or adolescents), any symptom-free intervals last no longer than
2 months (Criterion C). 
Prevalence
Persistent depressive disorder is effectively an amalgam of DSM-IV dysthymic disorder and
chronic major depressive episode. The 12-month prevalence in the United States is approxi-
mately 0.5% for persistent depre ssive disorder and 1.5% for chro nic major depressive disorder.
Development and Course
Persistent depressive disorder often has an early and insidious onset (i.e., in childhood,
adolescence, or early adult life) and, by de finition, a chronic course. Among individuals
with both persistent depressiv e disorder and borderline pers onality disorder, the covari-
ance of the corresponding features over ti me suggests the operatio n of a common mecha-
nism. Early onset (i.e., before age 21 years)  is associated with a higher likelihood of
comorbid personality disorder s and substance use disorders.
When symptoms rise to the level of a major depressive episode, they are likely to sub-
sequently revert to a lower level. However,  depressive symptoms are much less likely to
resolve in a given period of time in the context of persistent depressive disorder than they
are in a major depressive episode.
Risk and Prognostic Factors
Temperamental. Factors predictive of poorer long -term outcome include higher levels
of neuroticism (negative affect ivity), greater symptom severity, poorer global functioning,
and presence of anxiety disorders or conduct disorder.
Environmental. Childhood risk factors include parental loss or separation.
Genetic and physiological. There are no clear differences in  illness development, course,