The McNamara fallacy (also known as the quantitative fallacy), named for

Robert McNamara Robert Strange McNamara (; June 9, 1916 – July 6, 2009) was an American business executive and the eighth United States Secretary of Defense, serving from 1961 to 1968 under Presidents John F. Kennedy and Lyndon B. Johnson. He remains the Lis ...

, the

US Secretary of Defense The United States secretary of defense (SecDef) is the head of the United States Department of Defense, the executive department of the U.S. Armed Forces, and is a high ranking member of the federal cabinet. DoDD 5100.1: Enclosure 2: a The s ...

from 1961 to 1968, involves making a decision based solely on quantitative observations (or

metrics Metric or metrical may refer to: * Metric system, an internationally adopted decimal system of measurement * An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement Mathematics In mathema ...

) and ignoring all others. The reason given is often that these other observations cannot be proven. The fallacy refers to McNamara's belief as to what led the United States to defeat in the

Vietnam War The Vietnam War (also known by #Names, other names) was a conflict in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. It was the second of the Indochina Wars and was officially fought between North Vie ...

—specifically, his quantification of success in the war (e.g., in terms of enemy

body count A body count is the total number of people killed in a particular event. In combat, a body count is often based on the number of confirmed kills, but occasionally only an estimate. Often used in reference to military combat, the term can also r ...

), ignoring other variables.

Examples in warfare

The Vietnam War

The McNamara fallacy originates from the Vietnam War, in which enemy body counts were taken to be a precise and objective measure of success. War was reduced to a mathematical model: By increasing estimated enemy deaths and minimizing one's own, victory was assured. Critics note that

guerrilla warfare Guerrilla warfare is a form of irregular warfare in which small groups of combatants, such as paramilitary personnel, armed civilians, or Irregular military, irregulars, use military tactics including ambushes, sabotage, Raid (military), raids ...

, widespread resistance, and inevitable inaccuracies in estimates of enemy casualties can thwart this formula. McNamara's interest in quantitative figures is seen in

Project 100,000 Project 100,000, also known as McNamara's 100,000, McNamara's Folly, McNamara's Morons, and McNamara's Misfits, was a controversial 1960s program by the United States Department of Defense (DoD) to recruit soldiers who would previously have been ...

: by lowering admission standards to the military, enlistment was increased. Key to this decision was the idea that one soldier is, in the abstract, more or less equal to another, and that with the right training and superior equipment, he would factor positively in the mathematics of warfare. US Air Force Brigadier General

Edward Lansdale Edward Geary Lansdale (February 6, 1908 – February 23, 1987) was a United States Air Force officer until retiring in 1963 as a major general before continuing his work with the Central Intelligence Agency (CIA). Lansdale was a pioneer in cl ...

reportedly told McNamara, who was trying to develop a list of metrics to allow him to scientifically follow the progress of the war, that he was not considering the feelings of the common rural

Vietnamese people The Vietnamese people ( vi, người Việt, lit=Viet people) or Kinh people ( vi, người Kinh) are a Southeast Asian ethnic group native to modern-day Northern Vietnam and Dongxing, Guangxi, Southern China (Jing Islands, Dongxing, Guangxi ...

. McNamara wrote it down on his list in pencil, then erased it and told Lansdale that he could not measure it, so it must not be important.

The global war on terror

Donald Rumsfeld Donald Henry Rumsfeld (July 9, 1932 – June 29, 2021) was an American politician, government official and businessman who served as Secretary of Defense from 1975 to 1977 under president Gerald Ford, and again from 2001 to 2006 under Presi ...

, US Secretary of Defense under

George W. Bush George Walker Bush (born July 6, 1946) is an American politician who served as the 43rd president of the United States from 2001 to 2009. A member of the Republican Party, Bush family, and son of the 41st president George H. W. Bush, he ...

, sought to prosecute wars with better data, clear objectives, and achievable goals. Writes

Jon Krakauer Jon Krakauer (born April 12, 1954) is an American writer and mountaineer. He is the author of bestselling non-fiction books—'' Into the Wild''; ''Into Thin Air''; ''Under the Banner of Heaven''; and '' Where Men Win Glory: The Odyssey of Pat ...

In modern clinical trials

There has been increasing discussion of the McNamara fallacy in medical literature. In particular, the McNamara fallacy is invoked to describe the inadequacy of only using

progression-free survival Progression-free survival (PFS) is "the length of time during and after the treatment of a disease, such as cancer, that a patient lives with the disease but it does not get worse". In oncology, PFS usually refers to situations in which a tumor is p ...

(PFS) as a primary endpoint in clinical trials for agents treating metastatic solid tumors simply because PFS is an endpoint which is merely measurable, while failing to capture outcomes which are more meaningful, such as overall quality of life or overall survival.

In competitive admissions processes

In competitive admissions processes—such as those used for graduate medical education—evaluating candidates using only numerical metrics results in ignoring non-quantifiable factors and attributes which may ultimately be more relevant to the applicant's success in the position.

References