The theory of medicine, as of all other sciences, has often been affected by the personal equation—that constant error to which each individual is subject to a greater or less degree. Each observer, though he may be able to see facts clearly and even to trace the relation of cause and effect among them to some extent, is liable to error in the interpretation of those facts in proportion to the degree of his fixed personal bias, whether that personal bias be in favor of a widespread belief or merely of a little private theory of his own.
THE PERSONAL EQUATION IN MEDICINE. JAMA. 2009;302(20):2265. doi:10.1001/jama.2009.1628