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.
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. 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. This figure comports with recent estimates of the extent of mental illness in the population.