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Health psychology is the application of psychological theory and research to health, illness and health care. Whereas clinical psychology focuses on mental health and neurological illness, health psychology is concerned with the psychology of a much wider range of health-related behavior including healthy eating, the doctor-patient relationship, a patient's understanding of health information, and beliefs about illness. Health psychologists may be involved in public health campaigns, examining the impact of illness or health policy on quality of life or in research into the psychological impact of health and social care.