Major depressive disorder occurs throughout the life cycle. Longitudinal data suggest a changing pattern in the age of onset in the United States. In more recent birth cohorts, the rates of major depression were higher and the age of onset was younger. The lifetime prevalence rates for major depression per 100 population were determined in five US cities by the Epidemiologic Catchment Area Survey (ECA). The rates varied from a low of 2.9% in Baltimore to a high of 5.8% in New Haven. The mean lifetime prevalence rate in adults ages 18 and older for depression was reported as 4.4%. Weissman and Klerman reported data from international studies that found higher lifetime prevalence rates of depression in two nations: Canada (8.6%) and New Zealand (12.6%). Lower rates were observed in urban cities in Taiwan (0.9%) as well as in rural areas in Korea (1.0%). The lifetime prevalence rate of depression in Seoul, Korea was 3.4%. The rate of depression in Puerto Rico was established as 4.6%, a rate similar to the US mainland. Risk factors associated with major depressive disorder included female gender (rates in women were two to three times those of men), a positive family history of depression, urban residence, and a history of divorce and separation. These data are reported for international community surveys of mixed age populations.

The identification of major depressive disorder in the elderly is a complex task. Because of the number of medical illnesses and the number of prescribed medications being taken, the older person may experience changes in neurovegetative signs and changes in mood as the result of their illness and medications. Affective disorders (depression and dysphoria) may present in the elderly with cognitive impairment or somatic complaints, termed “masked depression.”

In a 1972 study of a stratified random sample of Durham County, North Carolina residents aged 65 and older, 14.7% were identified by the older American Resources and Services (OARS) Depression Scale as having substantial depressive symptoms. Thirty-three percent of this sample was black. Dysphoric symptoms were found in 4.5% of these community resident elderly. Some 3.7% had symptoms of major depression, but did not meet the full criteria for a diagnosis of depression. Only 1.8% met criteria for a diagnosis of major depression, and 1.9% had a secondary depressive disorder. Community residents with secondary depressive disorder who met the criteria for a diagnosis of depression had significant dysphoric symptoms and had evidence of cognitive dysfunction or a thought disorder. Only 1% of these older, depressed community residents was receiving therapy from a trained counselor. Factors associated with depression in this sample included being white and widowed, having impairment in social economic resources, having a history of alcohol abuse more often than nondepressed community residents, and having a greater tendency to use pain medications. Of the 14.7% of the sample with depressive symptoms, 44% had impaired physical health.

In a later survey of community residents age 55 and older completed in Kentucky in 1981, the Center for Epidemiologic Studies Depression Scale (CES-D) was used to screen the sample for the presence of depressive symptoms. Using a cutpoint of 29 (rather than the usual cutpoint of 16), 13.7% of men and 18.2% of women were identified as having symptoms of depression. Factors associated with symptoms of depression included older age, education of ≤4 years, income <$4000 per year, housing with ≤two rooms, being widowed, separated, or divorced, and poor health. The strongest association with depression in this sample was physical health. This finding was consistent with data from two prior studies.

These associations were confirmed by an analysis of the ECA sample of community residents aged 60 and older from Piedmont, North Carolina; 19% were diagnosed as having mild dysphoria, 4% had symptomatic depression, 2% had dysthymia, and 1.2% had a mixed depressive anxiety syndrome. Only 0.8% of this sample of older community residents had a diagnosis of major depression. The elderly with symptomatic depression reported poor physical health (3%), the loss of a loved one (25%), reported social phobias, and having experienced social isolation. Community residents with major depression and dysthymia were more likely to report poor physical health, subjective memory problems, subjective negative events, and difficulty with their support networks. The association of illness, disability, isolation, bereavement, and poverty with depression was confirmed by a study of Medicare recipients who resided in the Bronx, New York. Thus, epidemiologic studies of community resident elders in several US cities found a prevalence rate of major depression ranging from 0.8% to 1.8% and a rate for dysthymic disorder of 2%.

The rates of depressive symptoms among medically ill patients has been found to be higher. Stewart et al found 12% of severely medically ill inpatients had depressive illness. In 1967, Schwab et al studied a sample of hospitalized, medically ill patients. Using a clinic interview, depression screening instruments, and the medical record in order to determine the diagnosis, 22% of this sample was found to be depressed. Using the Zung Self-Rating Depression Scale, 42% of the sample of randomly selected outpatients was identified as depressed by clinical examination with only 30% screening positive for depression. Rates of depression among veterans ranged from 13% to 38%.

These data demonstrate that the rate of major depressive disorder is higher among medically ill patients, ranging from 12% to 42%, compared with the rates for various samples of community resident elderly (Table 1). The rate of major depression among medical patients is usually reported as 26%. The association between poor physical health, poverty, impaired support network, bereavement, ≤4 years of education, and an increased report of depressive symptoms and depressive disorders is important in the assessment of the older patient.

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