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Etiology (; alternatively aetiology) is the study of causation, or origination. The word is derived from the Greek , ''aitiologia'', "giving a reason for" (, ''aitia'', "cause"; and , ''-logia''). ==Description== In medicine, the term refers to the causes of diseases or pathologies.〔 Discusses several examples of the medical usage of the term ''etiology'' in the context of cleft lips and explains methods used to study causation.〕 Where no etiology can be ascertained, the disorder is said to be idiopathic. Traditional accounts of the causes of disease may point to the "evil eye".〔 〕 The Ancient Roman scholar Marcus Terentius Varro put forward early ideas about microorganisms in a 1st-century BC book titled ''On Agriculture''.〔''Varro On Agriculture'' 1,xii Loeb〕 Medieval thinking on the etiology of disease showed the influence of Galen and of Hippocrates.〔(Maimonides: an early but accurate view on the treatment of hemorrhoids -- Magrill and Sekaran 83 (979): 352 -- Postgraduate Medical Journal )〕 Medieval European doctors generally held the view that disease was related to the air and adopted a miasmatic approach to disease etiology.〔(Case study: the history and ethics clean air )〕 Etiological discovery in medicine has a history in Robert Koch's demonstration that the tubercle bacillus (''Mycobacterium tuberculosis'' complex) causes the disease tuberculosis, ''Bacillus anthracis'' causes anthrax, and ''Vibrio cholerae'' causes cholera. This line of thinking and evidence is summarized in Koch's postulates. But proof of causation in infectious diseases is limited to individual cases that provide experimental evidence of etiology. In epidemiology, several lines of evidence together are required to infer causation. Sir Austin Bradford-Hill demonstrated a causal relationship between smoking and lung cancer, and summarized the line of reasoning in the epidemiological criteria for causation. Dr. Al Evans, a US epidemiologist, synthesized his predecessors' ideas in proposing the Unified Concept of Causation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Etiology (medicine)」の詳細全文を読む スポンサード リンク
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