The Changing Rate of Major Depression

OBJECTIVE: To estimate temporal trends in the rates of major depression cross-nationally. DESIGN: Nine epidemiologic surveys and three family studies. SETTING AND PARTICIPANTS: Approximately 39,000 subjects in population-based samples from nine epidemiologic surveys, and 4000 relatives from three family studies that were conducted independently but using similar methodology in the 1980s in North America, Puerto Rico, Western Europe, the Middle East, Asia, and the Pacific Rim. OUTCOME MEASURES: Age at first onset of major depression by birth cohort and time period. RESULTS: There was an increase in the cumulative lifetime rates of major depression with each successively younger birth cohort at all sites with the exception of the Hispanic samples, in whom the rates in the older cohort (1915 through 1935) were approximately equal to those of the younger cohorts. However, results of fitting statistical models that separate period and cohort effects showed an overall increase in the rates of major depression over time over all countries, although the magnitude of the increase varied by country. The average relative risk of major depression between a particular cohort and the cohort born immediately before varied between 2.6 (95% confidence interval, 1.8 to 3.7) in Florence, Italy, and 1.3 (95% confidence interval, 1.2 to 1.4) in Christchurch, New Zealand. Short-term fluctuations in the rates of major depression during specific time periods and in specific cohorts also varied by country. CONCLUSIONS: Cross-nationally, the more recent birth cohorts are at increased risk for major depression. There are, however, variations in the long- and short-term trends for major depression by country, which suggests that the rates in these countries may have been affected by differing historical, social, economic, or biological environmental events. The linking of demographic, epidemiologic, economic, and social indices by country to these changes may clarify environmental conditions that influence the rates of major depression.