McNamara Fallacy

Origin and Yankelovich's four steps

McNamara built his reputation on statistical management at Ford Motor Company and in the US Army Air Forces' statistical control office. As defense secretary, he measured progress in the Vietnam War by the number of enemy soldiers killed, the body count. Gibson (1986) and Shapley (1993) documented this quantified management of the war in detail. In Kinnard's (1977) survey of US generals who served in Vietnam, many said body counts were inflated and invalid as a measure of progress. Comparing Vietnam and Korea, Gartner and Myers (1995) analyzed why body counts were adopted as a measure of success. The sociologist Daniel Yankelovich set out the fallacy in four steps, which Handy (1994) popularized. First, measure whatever can be easily measured. Second, disregard what cannot be easily measured, or give it an arbitrary value. Third, presume that what cannot be measured easily is not important. Fourth, say that what cannot be easily measured does not exist.

Distorted metrics and reactivity

The McNamara fallacy is intertwined with the way metrics themselves change behavior. Campbell (1979) argued that the more a quantitative social indicator is used for social decision-making, the more it is subject to corruption pressures and the more it distorts the social processes it was meant to monitor. This is Campbell's law. It echoes Goodhart's law, under which a measure ceases to be a good measure once it becomes a target. Kerr (1975) described the folly of organizations that hope for A while actually rewarding a more easily measured B. Bevan and Hood (2006) found that targets in the English public health system, such as waiting times, produced various forms of gaming to hit them. Espeland and Sauder (2007) showed the reactivity of US law school rankings, which led schools to reshape their behavior around ranking criteria.

Trust in numbers and the critique of metrics

Porter (1995) explained why numbers are trusted as symbols of objectivity: amid distrust of expert discretion, they lend public legitimacy. Analyzing audit in British universities, Strathern (1997) highlighted the problems that arise when a measure becomes a target. Basler (2009) used the McNamara fallacy to describe medical research's reliance on easily measured surrogate endpoints. In The Tyranny of Metrics, Muller (2018) argued that an excessive fixation on metrics in education, medicine, policing and the military erodes judgment and intrinsic motivation. The concept does not reject measurement itself. Rather, it warns against ignoring what cannot be measured. It also connects to the cobra effect, in which hitting a target ends up making a problem worse.

FAQ

What is the McNamara fallacy in simple terms?

It is the mistake of treating only what you can count as important and ignoring what you can't. The classic case is the Vietnam War, where progress was judged by enemy body counts while hard-to-measure factors such as popular support and the will to fight were missed.

How does the McNamara fallacy differ from Goodhart's law?

The McNamara fallacy focuses on the judgment error of ignoring what is hard to measure. Goodhart's law describes how, once a metric becomes a target, people change their behavior to meet it and the metric loses its meaning. The two concepts capture different sides of metric-driven management.

Sources reviewed: 2026-10-26

References

1. Kerr, S. (1975). On the folly of rewarding A, while hoping for B. Academy of Management Journal, 18(4), 769–783.
2. Kinnard, D. (1977). The War Managers. Hanover, NH: University Press of New England.
3. Campbell, D. T. (1979). Assessing the impact of planned social change. Evaluation and Program Planning, 2(1), 67–90.
4. Gibson, J. W. (1986). The Perfect War: Technowar in Vietnam. Boston: Atlantic Monthly Press.
5. Shapley, D. (1993). Promise and Power: The Life and Times of Robert McNamara. Boston: Little, Brown.
6. Handy, C. (1994). The Empty Raincoat: Making Sense of the Future. London: Hutchinson.
7. Gartner, S. S., & Myers, M. E. (1995). Body counts and "success" in the Vietnam and Korean wars. Journal of Interdisciplinary History, 25(3), 377–395.
8. Porter, T. M. (1995). Trust in Numbers: The Pursuit of Objectivity in Science and Public Life. Princeton: Princeton University Press.
9. Strathern, M. (1997). 'Improving ratings': Audit in the British university system. European Review, 5(3), 305–321.
10. Bevan, G., & Hood, C. (2006). What's measured is what matters: Targets and gaming in the English public health care system. Public Administration, 84(3), 517–538.
11. Espeland, W. N., & Sauder, M. (2007). Rankings and reactivity: How public measures recreate social worlds. American Journal of Sociology, 113(1), 1–40.
12. Basler, M. H. (2009). Utility of the McNamara fallacy. BMJ, 339, b3141.
13. Muller, J. Z. (2018). The Tyranny of Metrics. Princeton: Princeton University Press.