The medical model proposes that is it useful to think of abnormal behaviour as a disease. Became prominent in the 19/20th century, before which abnormal behaviour was based on superstition (thought to be possessed, victims of god"s punishment). Their disorder were thus treated with rituals such as chants, and exorcisms and were locked up in dungeons or killed if seen as dangerous. Thomas szasz is a critic of the medical model and says that strictly speaking disease can only affect the body, and abnormal behaviour usually involved a deviation from social norms rather than an illness. He contends that such problems are problems with living rather than medical problems. However, medical concepts such as diagnosis, prognosis, and etiology (causation and developmental history) have proven useful in the study of abnormality. Criteria of abnormal behaviour: deviance- as szasz said, people are said to have a disorder when their behaviour deviated from what society views as acceptable.