Bipolar disorder has a lifetime prevalence of approximately 1-3% according to population studies. The average age of onset is 25 years old, though onset can range from 12 to 65+ years old. Bipolar disorder is more common in urban populations and among those who are cohabiting, divorced or never married. A family history of bipolar disorder is also a risk factor. Earlier epidemiological studies found the prevalence of bipolar disorder did not differ by sex or ethnicity.