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April 26, 1976

Association vs Causation

Author Affiliations

Ethyl Corporation Baton Rouge, La

JAMA. 1976;235(17):1841. doi:10.1001/jama.1976.03260430017008

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To the Editor.—  It is unfortunate that we do not have as yet an animal model for studying chemicals that are presumed to cause aplastic anemia or other hematopoietic defects. It is difficult, therefore, to understand the conclusion by Dr Vodopick in her clinical report entitled "Cherchez la Chienne" (234:850, 1975). Despite her statement that "exposure to a chemical known to produce this effect is strong circumstantial evidence that it is the culprit," there is no evidence that y-benzene hexachloride causes bone marrow hypoplasia. There have been some reports of association with exposure to γ-benzene hexachloride, just as there have been reports of association with exposure to numerous other chemicals.Unfortunately, an association, particularly of this low order of magnitude, is of little value in coming to a conclusion as to causation. There is a common misconception that the benzene ring automatically must be looked on with suspicion as a