Evolving definitions of mental illness and wellness.

Understanding of the definitions of wellness and illness has changed from the mid-20th century to modern times, moving from a diagnosis-focused to a person-focused definition of mental illnesses, and from an "absence of disease" model to one that stresses positive psychological function for mental health. Currently, wellness refers to the degree to which one feels positive and enthusiastic about oneself and life, whereas illness refers to the presence of disease. These definitions apply to physical as well as mental illness and wellness.

Public health surveillance for mental health.

Public health systems have relied on public health surveillance to plan health programs, and extensive surveillance systems exist for health behaviors and chronic disease. Mental health has used a separate data collection system that emphasizes measurement of disease prevalence and health care use. In recent years, efforts to integrate these systems have included adding chronic disease measures to the Collaborative Psychiatric Epidemiology Surveys and depression measures to the Behavioral Risk Factor Surveillance System; other data collection systems have been similarly enhanced.