ROBERT B. PRICE, M.D., F.A.C.P.; Z. RENO VLAHCEVIC, M.D.
Differential diagnosis, like scientific research, is shown to be based on the method of hypothesis that was first described by Plato. The logical basis of this method is examined, potential fallacies of logic identified, and the process explained by Venn diagrams. To disprove a diagnosis because it fails to explain a finding, one must assume that there is only one unknown disease. To disprove a diagnosis because of lack of an expected finding, one must assume that this feature always accompanies that disease. A diagnosis is likely but unproved if the usual features of that disease are found and if the findings reflect the basic mechanism of the disease. It is emphasized, however, that compatible findings do not prove a diagnosis; they merely establish that it is possible. Proof demands the presence of a pathognomonic finding or of findings that, considered collectively, are uniquely characteristic of that disease and no other.
PRICE RB, VLAHCEVIC ZR. Logical Principles in Differential Diagnosis. Ann Intern Med. ;75:89–95. doi: 10.7326/0003-4819-75-1-89
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Published: Ann Intern Med. 1971;75(1):89-95.
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