Cross-national epidemiology of major depression and bipolar disorder.

Objective: To estimate the rates and patterns of major depression and bipolar disorder based on cross-national epidemiologic surveys.
Design and Setting: Population-based epidemiologic studies using similar methods from 10 countries: the United States, Canada, Puerto Rico, France, West Germany, Italy, Lebanon, Taiwan, Korea, and New Zealand.
Participants: Approximately 38000 community subjects.
Outcome Measures: Rates, demographics, and age at onset of major depression and bipolar disorder. Symptom profiles, comorbidity, and marital status with major depression.
Results: The lifetime rates for major depression vary widely across countries, ranging from 1.5 cases per 100 adults in the sample in Taiwan to 19.0 cases per 100 adults in Beirut. The annual rates ranged from 0.8 cases per 100 adults in Taiwan to 5.8 cases per 100 adults in New Zealand. The mean age at onset shows less variation (range, 24.8-34.8 years). In every country, the rates of major depression were higher for women than men. By contrast, the lifetime rates of bipolar disorder are more consistent across countries (0.3/100 in Taiwan to 1.5/100 in New Zealand); the sex ratios are nearly equal; and the age at first onset is earlier (average, 6 years) than the onset of major depression. Insomnia and loss of energy occurred in most persons with major depression at each site. Persons with major depression were also at increased risk for comorbidity with substance abuse and anxiety disorders at all sites. Persons who were separated or divorced had significantly higher rates of major depression than married persons in most of the countries, and the risk was somewhat greater for divorced or separated men than women in most countries.
Conclusions: There are striking similarities across countries in patterns of major depression and of bipolar disorder. The differences in rates for major depression across countries suggest that cultural differences or different risk factors affect the expression of the disorder.