Contributions of Epidemiology to Our Understanding of Bipolar Disorder

This chapter reviews the evidence on the prevalence, correlates, and burden of bipolar disorder from community-based surveys of general population samples. The pooled lifetime (12-month) prevalence for bipolar I disorder is about 1%, and for bipolar II disorder it is about 1.6%, with slightly lower rates for 12-month prevalence of about 0.7% and 0.5%, respectively. However, prevalence of the bipolar spectrum is substantially greater, approximating 5 to 6%. Rates of bipolar disorder are equivalent in males and females and do not differ substantially by ethnic status or social class. The onset of bipolar disorder occurs before age 18 years in about half of those who will eventually develop bipolar disorder, and by age 30 years in nearly all adults with this condition. Comorbidity is pervasive among both adolescents and adults with bipolar disorder in the general population, suggesting disturbances in multiple systems of emotion, cognition, and behavior. Population research has also highlighted the tremendous impact of bipolar disorder across levels of the individual, family, and society. Now that descriptive epidemiology has reached its maturity, ongoing research is providing information on risk factors, causal pathways, and consequences of bipolar disorder.