ITP is usually chronic in adults and the probability of durable remission is 20–40 percent.  The male to female ratio in the adult group varies from 1:1.2 to 1.7 in most age ranges (childhood cases are roughly equal for both genders) and the median age of adults at the diagnosis is 56–60.  The ratio between male and female adult cases tends to widen with age.  In the United States, the adult chronic population is thought to be approximately 60,000—with women outnumbering men approximately 2 to 1, which has resulted in ITP being designated an orphan disease.