Provided by David Satcher, M.D., Ph.D.
Surgeon General of the United States of America
Chapter 2
Epidemiology of Mental Illness
Few families in the United States are untouched by mental
illness. Determining just how many people have mental illness is one of the many
purposes of the field of epidemiology. Epidemiology is the study of patterns of
disease in the population. Among the key terms of this discipline, encountered
throughout this report, are incidence, which refers to new cases of a condition
which occur during a specified period of time, and prevalence, which refers to
cases (i.e., new and existing) of a condition observed at a point in time or
during a period of time. According to current epidemiological estimates, at
least one in five people has a diagnosable mental disorder during the course of
a year (i.e., 1-year prevalence).
Epidemiological estimates have shifted over time because of changes in the
definitions and diagnosis of mental health and mental illness. In the early
1950s, the rates of mental illness estimated by epidemiologists were far higher
than those of today. One study, for example, found 81.5 percent of the
population of Manhattan, New York, to have had signs and symptoms of mental
distress (Srole, 1962). This led the authors of the study to conclude that
mental illness was widespread. However, other studies began to find lower rates
when they used more restrictive definitions that reflected more contemporary
views about mental illness. Instead of classifying anyone with signs and
symptoms as being mentally ill, this more recent line of epidemiological
research only identified people as mentally ill if they had a cluster of signs
and symptoms that, when taken together, impaired people’s ability to function (Pasamanick,
1959; Weissman et al., 1978). By 1978, the President’s Commission on Mental
Health (1978) concluded conservatively that the annual prevalence of specific
mental disorders in the United States was about 15 percent. This figure comports
with recent estimates of the extent of mental illness in the population. Even as
this figure has become more sharply delineated, the older and larger estimates
underscore the magnitude of mental distress in the population, which this report
refers to as “mental health problems.”
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