McNamara fallacy

The McNamara fallacy (also known as the quantitative fallacy),^[1] named for Robert McNamara, the US Secretary of Defense from 1961 to 1968, involves making a decision based solely on quantitative observations (or metrics) and ignoring all others. The reason given is often that these other observations cannot be proven.

But when the McNamara discipline is applied too literally, the first step is to measure whatever can be easily measured. The second step is to disregard that which can't easily be measured or given a quantitative value. The third step is to presume that what can't be measured easily really isn't important. The fo[u]rth step is to say that what can't be easily measured really doesn't exist. This is suicide.
— Daniel Yankelovich, "Interpreting the New Life Styles", Sales Management (1971)^[2]

The quote originally referred to McNamara's ideology during the two months that he was president of Ford Motor Company, but has since been interpreted to refer to his attitudes during the Vietnam War.

^ Fischer, D. H. (June 1970). Historians' fallacies: toward a logic of historical thought. Harper torchbooks (first ed.). New York: HarperCollins. p. 90. ISBN 978-0-06-131545-9. OCLC 185446787.
^ Yankelovich, Daniel (November 15, 1971). "Interpreting the New Life Styles". Sales Management, the Marketing Magazine. Dartnell Corporation. Retrieved March 11, 2023.

[1] Fischer, D. H. (June 1970). Historians' fallacies: toward a logic of historical thought. Harper torchbooks (first ed.). New York: HarperCollins. p. 90. ISBN 978-0-06-131545-9. OCLC 185446787.

[2] Yankelovich, Daniel (November 15, 1971). "Interpreting the New Life Styles". Sales Management, the Marketing Magazine. Dartnell Corporation. Retrieved March 11, 2023.

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