Patterns in the Population
Depression affects 7% of the population, including 10% of the population over the age of 18, during a single year. In the U.S., 19 million people will suffer from mood disorders this year.
Major depression is a major cause of disability in the U.S. and worldwide. Unipolar major depression is second only to coronary heart disease as the major illness contributing to disability in major market economies, and unipolar major depression accounts for 7% of disability adjusted life years, an international standard measure of disability.
This year, 12% of American women and 7% of American men will experience depression. Over their lifetimes, approximately 20% of women and 10% of men will experience major depression. Whether examined for one year or for the entire life span, approximately twice as many women as men will be affected. Women between the ages of 18 and 45 compose the largest proportion of people with major depression.
In the U.S., two large studies provided estimates of the numbers of people experiencing major depression and mild-to-moderate depression (dysthymia). These studies were the Epidemiologic Catchman Area (ECA) study of mental health in America and the National Comorbidity Study (NCS). The following table displays the major findings on the prevalence of depression:
| ECA Study | NCS | ||||||||
| Mild-to-Moderate Depression |
Major Depression | Mild-to-Moderate Depression |
Major Depression | ||||||
| Lifetime | Past Year | Lifetime | Past Year | Lifetime | Past Year | Lifetime | Past Year | ||
| Total | 3.2 | N/A | 4.9 | 2.7 | Total | 6.4 | 2.5 | 14.9 | 8.6 |
| Male | 2.2 | N/A | 2.6 | 1.4 | Male | 4.8 | 2.1 | 11.0 | 6.1 |
| Female | 4.1 | N/A | 7.0 | 4.0 | Female | 8.0 | 3.0 | 18.6 | 11.0 |
For major depression, estimates of prevalence rates vary widely. The lifetime prevalence rate found in the ECA study was 4.9%. Much higher rates, however, also have been reported, such as that assessed in the NCS at 14.9%. Depression was the most common psychiatric disorder among those evaluated in the NCS (Kessler and Zhao 1999). The lifetime prevalence of dysthymia has been estimated at 3.2% by the ECS study (Kaelber et al 1995; Keller 1994) and at 6.4% by the NCS (Kessler and Zhao 1999).
There are obvious differences in prevalence estimates between the two landmark studies on mental health in the U.S. The discrepancies are likely due to variations in methodology, diagnostic criteria, instruments, age composition, and year of study. Compared to the ECA study, the NCS provides more recent data and a more representative sample (Kessler and Zhao 1999). Given the greater limitations of the ECA study, the higher estimates of the NCS are probably more accurate.
